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PubMed2001

Identification of 66 box C/D snoRNAs in Arabidopsis thaliana: extensive gene duplications generated multiple isoforms predicting new ribosomal RNA 2'-O-methylation sites.

Dozens of box C/D small nucleolar RNAs (snoRNAs) have recently been found in eukaryotes (vertebrates, yeast), ancient eukaryotes (trypanosomes) and archae, that specifically target ribosomal RNA sites for 2'-O-ribose methylation. Although early biochemical data revealed that plant rRNAs are among the most highly ribomethylated in eukaryotes, only a handful of methylation guide snoRNAs have been characterized in this kingdom. We report 66 novel box C/D snoRNAs identified by computational screening of Arabidopsis genomic sequences that are expressed in vivo from either single genes, 17 different clusters or three introns. At the structural level, many box C/D snoRNAs have dual antisense elements often matching rRNA regions close to each other on the rRNA secondary structure, which is reminiscent of their archaeal counterparts. Remarkable specimens are found that display two antisense elements having the potential to form an extended snoRNA-rRNA duplex of 23 to 30 nt, in line with the hypothetical function of box C/D snoRNAs in pre-rRNA folding or chaperoning. In contrast to other species, many Arabidopsis snoRNAs are found in multiple isoforms mainly resulting from two different mechanisms: large chromosomal duplications and small tandem duplications producing polycistronic genes. The discovery of numerous different snoRNAs, some of them arising from common ancestors, provide new insights to understand snoRNAs evolution and the birth of new rRNA methylation sites in plants and other organisms.

Arabidopsis↗

PubMed1999

The mitochondrial RNA ligase from Leishmania tarentolae can join RNA molecules bridged by a complementary RNA.

A biochemical characterization was performed with a partially purified RNA ligase from isolated mitochondria of Leishmania tarentolae. This ligase has a K(m) of 25 +/- 0.75 nM and a V(max) of 1.0 x 10(-4) +/- 2.4 x 10(-4) nmol/min when ligating a nicked double-stranded RNA substrate. Ligation was negatively affected by a gap between the donor and acceptor nucleotides. The catalytic efficiency of the circularization of a single-stranded substrate was 5-fold less than that of the ligation of a nicked substrate. These properties of the mitochondrial RNA ligase are consistent with an expected in vivo role in the process of uridine insertion/deletion RNA editing, in which the mRNA cleavage fragments are bridged by a cognate guide RNA.

Adenosine Triphosphate↗

PubMed2004

Substrate specificity for 4-thiouridine modification in Escherichia coli.

The biosynthesis of 4-thiouridine (s4U) in Escherichia coli tRNA requires the action of both the thiamin pathway enzyme ThiI and the cysteine desulfurase IscS. IscS catalyzes sulfur transfer from l-cysteine to ThiI, which utilizes Mg-ATP to activate uridine 8 in tRNA and transfers sulfur to give s4U. In this work, we show through deletion analysis of unmodified E. coli tRNA(Phe) that the minimum substrate for s4U modification is a mini-helix comprising the stacked acceptor and T stems containing an internal bulged region. The size of the bulged loop must be at least 4 nucleotides and contain the target uridine as the first nucleotide. Replacement of the T loop sequence with a tetraloop in the deletion substrate increases activity and shows that the TpsiC primary sequence is not a recognition element. An unmodified tRNA(Phe) transcript in which the 3'-terminal ACCA sequence is removed to give a blunt terminus has <0.1% activity, although the addition of a single overhanging base essentially restores activity. In addition, reducing the distance of the 3' terminus relative to U8 by as little as 1 bp severely impairs activity. By dissecting a minimal RNA substrate in the T loop region, a two-piece system consisting of a substrate RNA and a "guide" RNA is efficiently modified. Our results indicate that outside of the modified U8, there is no primary sequence requirement for substrate recognition. However, the secondary and tertiary structure restrictions appear sufficient to explain why s4U modification is limited in the cell to tRNA.

Bacterial Proteins↗

PubMed2002

Single gene target bacterial identification. groEL gene sequencing for discriminating clinical isolates of Burkholderia pseudomallei and Burkholderia thailandensis.

Proper identification of Burkholderia pseudomallei and Burkholderia thailandensis is crucial in guiding clinical management of patients with suspected melioidosis, as more than 99% of cases of melioidosis are caused by B. pseudomallei, whereas B. thailandensis is only responsible for causing less than 1% of the cases. However, the difference between the 16S ribosomal RNA gene sequences of B. pseudomallei and that of B. thailandensis is only 1%, and is therefore not discriminative enough for distinguishing the 2 species confidently. In this study, we amplified and sequenced the groEL genes of 7 strains of B. thailandensis and 6 strains of B. pseudomallei, and compared the sequences with 7 other groEL gene sequences of Burkholderia species. BLAST analysis revealed that the putative protein encoded by the groEL gene of B. thailandensis has 99.6%, 99.5%, 98.4%, 98.5%, and 96.5% amino acid identity with the groEL of B. pseudomallei, B. mallei, B. cepacia, B. vietnamiensis, and B. fungorum respectively. The amino acid sequences of GroEL of the strains of B. thailandensis and B. pseudomallei all showed >99.5% amino acid identity with each other. The nucleotide sequence of the groEL gene of any of the strains of B. thailandensis showed >99.8% nucleotide identity with that of any of the other strains of B. thailandensis, and the nucleotide sequence of the groEL gene of any of the strains of B. pseudomallei showed >99.5% nucleotide identity with that of any of the other strains of B. pseudomallei. However, the nucleotide sequence of any of the strains of B. thailandensis showed <97.6% nucleotide identity with any of the strains of B. pseudomallei. The amino acid sequences of GroEL of the 20 strains of Burkholderia species all showed >96% amino acid identity with each other. Furthermore, the nucleotide sequence of the groEL genes of the 2 strains of B. cepacia showed >99.5% nucleotide identity with each other, and the nucleotide sequence of the groEL gene of B. mallei showed >99.5% nucleotide identity with any of the strains of B. pseudomallei. The groEL gene sequence is therefore good for distinguishing between B. thailandensis and B. pseudomallei, and the GroEL amino acid and groEL nucleotide sequences of this single gene locus may potentially be useful for a 2-tier hierarchical identification of medically important Burkholderia at the genus and species levels respectively.

Base Sequence↗

PubMed2006

Plasma HIV-1 RNA to guide patient selection for antiretroviral therapy in resource-poor settings: efficiency related to active case finding.

Scaling up access to highly active antiretroviral therapy (HAART) requires eligibility criteria that safeguard treatment efficiency in resource-poor settings. We determined whether supply of HAART on the basis of plasma viral load testing could result in a stronger reduction of AIDS incidence as compared with CD4 count-driven strategies. Expected AIDS incidence rates corresponding to distinct HAART eligibility criteria were calculated by relying on risk parameters obtained through the Amsterdam cohort studies on HIV infection and AIDS. We modeled 2 different treatment settings derived from sub-Saharan African surveys. In a hospital-based setting, the reduction in the 1-year AIDS incidence is the same for any HAART administration rate if patients are selected on a single CD4 cell count criterion or on (additional) criteria for plasma HIV-1 RNA. In a community-based setting, where patients are identified at less advanced stages of infection, the reduction in the 1-year AIDS incidence is higher at particular HAART administration rates if patients are selected on criteria for plasma HIV-1 RNA rather than CD4 cell count. Plasma viral load testing can ensure a more efficient allocation of antiretroviral therapy but only when applied to a strategy of active case finding in the community.

Acquired Immunodeficiency Syndrome↗

PubMed2026

scGPA: an LLM-assisted workflow for directional virtual gene perturbation analysis from single-cell transcriptomes.

BACKGROUND: Existing virtual perturbation methods can often infer directional changes by comparing predicted post-perturbation expression profiles with control cells. However, workflows that directly return direction-specific downstream candidate genes together with confidence scores, evidence support and interpretable summaries remain limited. We developed scGPA, an LLM-assisted workflow system for directional single-cell virtual gene perturbation analysis. METHODS: scGPA starts from raw single-cell RNA sequencing data and performs quality control, normalization, dimensionality reduction, clustering and cell-group selection. It then constructs cell-group-specific wild-type regulatory networks using repeated subsampling, principal component regression (PCR)/Ridge-based network inference and CP tensor denoising. Based on these networks, scGPA simulates dose-aware virtual knockdown of the target gene and applies signed perturbation propagation to estimate the magnitude and direction of downstream transcriptional responses. LLM assistance is used for marker-based cell-type annotation, evidence-guided candidate prioritization and user-facing biological summarization. RESULTS: We benchmarked scGPA across five public Perturb-seq datasets and compared its performance with GEARS, scGPT and a random baseline. The overall correct prediction rate of scGPA was 23.0%, exceeding those of GEARS (20.7%), scGPT (15.1%) and the random baseline (13.6%). These results indicate that scGPA achieved a higher correct prediction rate than the two comparator models and the random baseline. We subsequently evaluated scGPA using a public osteosarcoma single-cell dataset and performed qRT-PCR validation in 143B osteosarcoma cells. Among genes with significant experimental changes, scGPA achieved a directional concordance of 76.9%. When all tested downstream genes were counted, 37.0% were directionally correct, 51.9% showed no significant change and 11.1% changed in the opposite direction. CONCLUSIONS: scGPA provides a practical workflow system for predicting and prioritizing direction-specific downstream transcriptional responses after target-gene perturbation. By integrating single-cell regulatory network inference, signed virtual perturbation and LLM-assisted interpretation, scGPA supports target-gene function inference and downstream mechanistic investigation from single-cell transcriptomic data.

Single-Cell Gene Expression Analysis↗

PubMed1991

Trypanosoma equiperdum minicircles encode three distinct primary transcripts which exhibit guide RNA characteristics.

The mitochondrial DNA of trypanosomes is composed of maxicircle and minicircle DNAs catenated into a network, called the kinetoplast. Maxicircles encode proteins and RNAs necessary for mitochondrial assembly. Minicircles encode small transcripts which are believed to serve as guide RNAs in the process of RNA editing of maxicircle transcripts. Trypanosoma equiperdum minicircles contain three transcription units which produce three distinct transcripts. The genes for these transcripts are flanked by imperfect 18-bp repeats separated by approximately 110 bp. The transcripts have a 5' triphosphate, indicating that they are primary transcripts. Minicircle transcription initiates at a purine within a conserved sequence, 5'-AYAYA-3', where Y is a pyrimidine, 32 bp from the upstream inverted repeat, suggesting that the repeats may function in transcript initiation. Transcripts from a single minicircle transcription unit range in size from 55 to 70 nucleotides. This size heterogeneity within a single sequence class is due to the variable length of nontemplated uridine residues composing a 3' tail. The size range and heterogeneous polyuridylate 3' end of the minicircle transcripts appear to be conserved features and may be related to transcript function.

Animals↗

PubMed2005

The K-loop, a general feature of the Pyrococcus C/D guide RNAs, is an RNA structural motif related to the K-turn.

The C/D guide RNAs predicted from the genomic sequences of three species of Pyrococcus delineate a family of small non-coding archaeal RNAs involved in the methylation of rRNA and tRNA. The C/D guides assemble into ribonucleoprotein (RNP) that contains the methyltransferase. The protein L7Ae, a key structural component of the RNP, binds to a Kink-turn (K-turn) formed by the C/D motif. The K-turn is a structure that consists of two RNA stems separated by a short asymmetric loop with a characteristic sharp bend (kink) between the two stems. The majority of the pyrococcal C/D guides contain a short 3 nt-spacer between the C'/D' motifs. We show here that conserved terminal stem-loops formed by the C'/D' motif of the Pyrococcus C/D RNAs are also L7Ae-binding sites. These stem-loops are related to the K-turn by sequence and structure, but they consist of a single stem closed by a terminal loop. We have named this structure the K-loop. We show that conserved non-canonical base pairs in the stem of the K-loop are necessary for L7Ae binding. For the C/D guides with a 3 nt-spacer we show that the sequence and length is also important. The K-loop could improve the stability of the C/D guide RNAs in Pyrococcal species, which are extreme hyperthermophiles.

Archaeal Proteins↗

PubMed2027

Systematic Dissection of Key Driver Perturbation Signatures in Single Cells via ECCITE-seq.

CRISPR screens, such as expanded CRISPR-compatible cellular indexing of transcriptomes and epitopes by sequencing (ECCITE-seq), enable the simultaneous measurement of transcriptomes, gRNA identity, and cell-surface protein expression at single-cell resolution to systematically interrogate gene function. This platform provides a powerful and scalable experimental approach for validating disease-associated regulators identified by large-scale association studies and other computational methods, including network-based analyses of multi-omics data. Here, as an example application, we describe an ECCITE-seq framework to characterize the transcriptomic consequences of perturbing multiple neuronal key driver genes associated with Alzheimer's disease (AD) in human-induced pluripotent stem cell (hiPSC)-derived neurons. More broadly, by integrating customized pooled gRNA libraries with different CRISPR effectors across multiple cell types, this approach allows for the assessment of the regulatory impact of candidate genes implicated in development and disease processes.

Humans↗

PubMed2026

Novel insights into retinoblastoma: From oncogenic circuitry to precision diagnosis and eye-preserving therapies.

Retinoblastoma (RB) represents the most common primary intraocular malignancy in childhood and stands as a paradigm for translating molecular oncology into precision clinical management. This review synthesizes the comprehensive evolution in the understanding and treatment of RB. First, we deconstruct the intricate oncogenic circuitry that extends far beyond Knudson's classic "two-hit" RB1 inactivation model, describing non-classical MYCN-driven pathogenesis, multi-layered epigenetic reprogramming (including chromatin, RNA and histone changes), and distinct histological subtypes with defined clinical correlates, such as the favorable-prognosis cavitary RB. Single-cell genomics has elucidated the cellular origin from cone precursor cells and intratumoral heterogeneity. Risk stratification has been refined through well-defined classification systems, from the therapy-guiding International Intraocular Retinoblastoma Classification (IIRC) to the comprehensive American Joint Committee on Cancer Tumor-Node-metastasis (AJCC TNM) staging. Furthermore, the diagnostic paradigm has advanced from conventional anatomical imaging to liquid biopsies, enabling non-invasive molecular staging and monitoring via tumor-derived cell-free DNA analysis. Concurrently, the therapeutic landscape has undergone a radical shift, moving from enucleation and external-beam radiotherapy to an era dominated by local sight-preserving strategies. We provide a critical synthesis of the evidence for intravenous chemotherapy and the transformative role of super-selective intra-arterial chemotherapy (IAC), and describe essential randomized controlled trials, technical innovations, and optimized drug regimens. Finally, we explore emerging targeted molecular therapies and future directions. By integrating cutting-edge molecular insights with robust, high-level clinical evidence, this review offers the framework for achieving patient and eye survival as well as vision preservation in children with Retinoblastoma.

Intra-arterial chemotherapy↗

PubMed1998

A phase I study of adenovirus-mediated wild-type p53 gene transfer in patients with advanced non-small cell lung cancer.

Mutations of the tumor suppressor gene p53 are the most common genetic alterations observed in human cancer. Loss of wild-type p53 function impairs cell cycle arrest as well as repair mechanisms involved in response to DNA damage. Further, apoptotic pathways as induced by radio- or chemotherapy are also abrogated. Gene transfer of wild-type p53 was shown to reverse these deficiencies and to induce apoptosis in vitro and in preclinical in vivo tumor models. A phase I dose escalation study of a single intratumoral injection of a replication-defective adenoviral expression vector encoding wild-type p53 was carried out in patients with incurable non-small cell lung cancer. All patients enrolled had p53 protein overexpression as a marker of mutant p53 status in pretreatment tumor biopsies. Treatment was performed either by bronchoscopic intratumoral injection or by CT-guided percutaneous intratumoral injection of the vector solution. Fifteen patients were enrolled in two centers, and were treated at four different dose levels ranging from 10(7) to 10(10) PFU (7.5 x 10(9) to 7.5 x 10(12) particles). No clinically significant toxicity was observed. Successful transfer of wild-type p53 was achieved only with higher vector doses. Vector-specific wild-type p53 RNA sequences could be demonstrated in posttreatment biopsies of six patients. Transient local disease control by a single intratumoral injection of the vector solution was observed in four of those six successfully transduced patients. There was no evidence of clinical responses at untreated tumor sites. Wild-type p53 gene therapy by intratumoral injection of a replication-defective adenoviral expression vector is safe, feasible, and biologically effective in patients with advanced non-small cell lung cancer.

Adenoviridae↗

PubMed2006

Structure of Aquifex aeolicus argonaute highlights conformational flexibility of the PAZ domain as a potential regulator of RNA-induced silencing complex function.

Gene silencing mediated by RNA interference requires the sequence-specific recognition of target mRNA by the endonuclease Argonaute, the primary enzymatic component of the RNA-induced silencing complex. We report the crystal structure of Aquifex aeolicus Argonaute, refined at 3.2A resolution. Relative to recent Argonaute structures, a 24 degrees reorientation of the PAZ domain in our structure opens a basic cleft between the N-terminal and PAZ domains, exposing the guide strand binding pocket of PAZ. This rearrangement leads to a branched, Y-shaped system of grooves that extends through the molecule and merges in a central channel containing the catalytic residues. A 5.5-ns molecular dynamics simulation of Argonaute shows a strong tendency of the PAZ and N-terminal domains to be mobile. Binding of single-stranded DNA to Argonaute monitored by total internal reflection fluorescence spectroscopy shows biphasic kinetics, also indicative of domain rearrangement upon DNA binding. Conformational rearrangement of the PAZ domain may therefore be critical for the catalytic cycle of Argonaute and the RNA-induced silencing complex.

Bacteria↗

PubMed2025

Rapid Generation of Recombinant Poxviruses Using CRISPR/Cas9 Gene Editing.

The low-frequency natural recombination that is detected in poxvirus-infected cells has long been used to genetically modify poxviruses. Such recombinant poxviruses have found many applications as vaccines for preventing infectious diseases and as experimental cancer therapeutics. Unfortunately, these methods are time consuming, can leave behind "scars" or selectable markers, and many months of work may be required to generate plaque-purified recombinants bearing multiple virus gene substitutions, deletions, and/or inserted transgenes. Over the last decade, several reports have described how CRISPR/Cas9 technologies can be used to better facilitate genetic manipulation of vaccinia virus (VACV). These protocols use Cas9/gRNA complexes to introduce double-stranded breaks into specific sites in virus genomic DNA either in vivo or in vitro. Recombination-repair reactions are then employed to repair the breaks using transfected DNAs encoding the required homologies and desired mutation(s). Here we describe a method where we combine CRISPR/Cas9 genome editing in vitro, followed by Leporipoxvirus-catalyzed repair and reactivation of the cut VACV DNA using repair fragments provided in trans. This method optimizes several steps in the preparation of the CRISPR/Cas9-cut VACV DNA and can be used to introduce mutations at multiple sites without requiring selectable markers. It also provides some guidance regarding how the position of the CRISPR/Cas9-cuts can affect co-conversion of flanking markers embedded in the repair fragment. The method allows researchers to quickly generate recombinant VACV bearing multiple genetic alterations and using only a single round of reactivation and plating.

CRISPR-Cas Systems↗

PubMed2000

Evidence that processed small dsRNAs may mediate sequence-specific mRNA degradation during RNAi in Drosophila embryos.

BACKGROUND: RNA interference (RNAi) is a phenomenon in which introduced double-stranded RNAs (dsRNAs) silence gene expression through specific degradation of their cognate mRNAs. Recent analyses in vitro suggest that dsRNAs may be copied, or converted, into 21-23 nucleotide (nt) guide RNAs that direct the nucleases responsible for RNAi to their homologous mRNA targets. Such small RNAs are also associated with gene silencing in plants. RESULTS: We developed a quantitative single-embryo assay to examine the mechanism of RNAi in vivo. We found that dsRNA rapidly induced mRNA degradation. A fraction of dsRNAs were converted into 21-23 nt RNAs, and their time of appearance and persistence correlated precisely with inhibition of expression. The strength of RNAi increased disproportionately with increasing dsRNA length, but an 80bp dsRNA was capable of effective gene silencing. RNAi was saturated at low dsRNA concentration and inhibited by excess unrelated dsRNA. The antisense strand of the dsRNA determined target specificity, and excess complementary sense or antisense single-stranded RNAs (ssRNAs) competed with the RNAi reaction. CONCLUSIONS: Processed dsRNAs can act directly to mediate RNAi, with the antisense strand determining mRNA target specificity. The involvement of 21-23 nt RNAs is supported by the kinetics of the processing reaction and the observed size dependence. RNAi depends on a limiting factor, possibly the nuclease that generates the 21-23 mer species. The active moiety appears to contain both sense and antisense RNA strands.

Animals↗

PubMed1998

RNA editing: trypanosomes rewrite the genetic code.

The understanding of how genetic information is stored and expressed has advanced considerably since the "central dogma" asserted that genetic information flows from the nucleotide sequence of DNA to that of messenger RNA (mRNA) which in turn specifies the amino acid sequence of a protein. It was found that genetic information can be stored as RNA (e.g. in RNA viruses) and can flow from RNA to DNA by reverse transcriptase enzyme activity. In addition, some genes contain introns, nucleotide sequences that are removed from their RNA (by RNA splicing) and thus are not represented in the resultant protein. Furthermore, alternative splicing was found to produce variant proteins from a single gene. More recently, the study of trypanosome parasites revealed an unexpected and indeed counter-intuitive genetic complexity. Genetic information for a single protein can be dispersed among several (DNA) genes in these organisms. One of these genes specifies an encrypted precursor mRNA that is converted to a functional mRNA by a process called RNA editing that inserts and deletes uridylate nucleotides. The sequence of the edited mRNA is specified by multiple small RNAs, named guide RNAs, (gRNAs) each of which is encoded in a separate gene. Thus, edited mRNA sequences are assembled from multiple genes by the transfer of information from one type of RNA to another. The existence of editing was surprising but has stimulated the discovery of other types of RNA editing. The Stuart laboratory has been exploring RNA editing in trypanosomes from the time of its discovery. They found dramatic differences between the mitochondrial gene sequences and those of the corresponding mRNAs, which indicated editing by the insertion and deletion of uridylates. Some editing was modest; simply eliminating shifts in sequence register of minimally extending the protein coding sequence. However, editing of many mRNAs was startingly extensive. The RNA sequence was essentially entirely remodeled with its sequence more the result of editing than the gene sequence. The identities of genes for such extensively edited RNA were not recognizable from the DNA sequence but they were readily identifiable from the edited mRNA sequence. Thus, despite the complex and extensive editing the resultant mRNA sequence is precise. Characterization of partially edited RNAs indicated that editing proceeds in the direction opposite to that used to specify the protein which reflects the use of the gRNAs. The numerous gRNAs that are used for editing are encoded in the DNA molecules whose role was previously a mystery. Using information gained in our earlier studies, the Stuart group developed an in vitro system that reproduces the fundamental process of editing in order to resolve the mechanism by which it occurs. They determined that editing entails a series of enzymatic steps rather than the mechanism used in RNA splicing. They also showed that chimeric gRNA-mRNA molecules are aberrant by-products of editing rather than intermediates in the process as had been proposed. Additional studies are exploring precisely how the number of added and deleted uridylates is specified by the gRNA. The Stuart laboratory showed that editing is performed by an aggregation of enzymes that catalyze the separate steps of editing. It also developed a method to purify this multimolecule complex that contains several, perhaps tens of, proteins. This will allow the study of its composition and the functions of its component parts. Indeed, the gene for one component has been identified and its detailed characterization begun. These studies are developing tools to explore related processes. An early finding in the lab was that the various mRNAs are differentially edited during the life cycle of the parasite. The pattern of this editing indicates that editing serves to regulate the alternation between two modes of energy generation. This regulation is coordinated with other events that are occurring during the life c

Animals↗

PubMed2004

Redundancy of the two dicer genes in transgene-induced posttranscriptional gene silencing in Neurospora crassa.

RNA interference (RNAi) in animals, cosuppression in plants, and quelling in fungi are homology-dependent gene silencing mechanisms in which the introduction of either double-stranded RNA (dsRNA) or transgenes induces sequence-specific mRNA degradation. These phenomena share a common genetic and mechanistic basis. The accumulation of short interfering RNA (siRNA) molecules that guide sequence-specific mRNA degradation is a common feature in both silencing mechanisms, as is the component of the RNase complex involved in mRNA cleavage. During RNAi in animal cells, dsRNA is processed into siRNA by an RNase III enzyme called Dicer. Here we show that elimination of the activity of two Dicer-like genes by mutation in the fungus Neurospora crassa eliminates transgene-induced gene silencing (quelling) and the processing of dsRNA to an siRNA form. The two Dicer-like genes appear redundant because single mutants are quelling proficient. This first demonstration of the involvement of Dicer in gene silencing induced by transgenes supports a model by which a dsRNA produced by the activity of cellular RNA-dependent RNA polymerases on transgenic transcripts is an essential intermediate of silencing.

Base Sequence↗

PubMed2005

Unique mitochondrial genome structure in diplonemids, the sister group of kinetoplastids.

Kinetoplastid flagellates are characterized by uniquely massed mitochondrial DNAs (mtDNAs), the kinetoplasts. Kinetoplastids of the trypanosomatid group possess two types of mtDNA molecules: maxicircles bearing protein and mitoribosomal genes and minicircles specifying guide RNAs, which mediate uridine insertion/deletion RNA editing. These circles are interlocked with one another to form dense networks. Whether these peculiar mtDNA features are restricted to kinetoplastids or prevail throughout Euglenozoa (euglenids, diplonemids, and kinetoplastids) is unknown. Here, we describe the mitochondrial genome and the mitochondrial ultrastructure of Diplonema papillatum, a member of the diplonemid flagellates, the sister group of kinetoplastids. Fluorescence and electron microscopy show a single mitochondrion per cell with an ultrastructure atypical for Euglenozoa. In addition, DNA is evenly distributed throughout the organelle rather than compacted. Molecular and electron microscopy studies distinguish numerous 6- and 7-kbp-sized mitochondrial chromosomes of monomeric circular topology and relaxed conformation in vivo. Remarkably, the cox1 gene (and probably other mitochondrial genes) is fragmented, with separate gene pieces encoded on different chromosomes. Generation of the contiguous cox1 mRNA requires trans-splicing, the precise mechanism of which remains to be determined. Taken together, the mitochondrial gene/genome structure of Diplonema is not only different from that of kinetoplastids but unique among eukaryotes as a whole.

Animals↗

PubMed1995

Minicircle-encoded guide RNAs from Crithidia fasciculata.

Although the mitochondrial uridine insertion/deletion, guide RNA (gRNA)-mediated type of RNA editing has been described in Crithidia fasciculata, no evidence for the encoding of gRNAs in the kinetoplast minicircle DNA has been presented. There has also been a question as to the capacity of the minicircle DNA in this species to encode the required variety of gRNAs, because the kinetoplast DNA from the C1 strain has been reported as essentially containing a single minicircle sequence class. To address this problem, the genomic and mature edited sequences of the MURF4 and RPS12 cryptogenes were determined and a gRNA library was constructed from mitochondrial RNA. Five specific gRNAs were identified, two of which edit blocks within the MURF4 mRNA, and three of which edit blocks within the RPS12 mRNA. The genes for these gRNAs are all localized with identical polarity within one of the two variable regions of specific minicircle molecules, approximately 60 bp from the "bend" region. These minicircles were found to represent minor sequence classes representing approximately 2% of the minicircle DNA population in the network. The major minicircle sequence class also encodes a gRNA at the same relative genomic location, but the editing role of this gRNA was not determined. These results confirm that kinetoplast minicircle DNA molecules in this species encode gRNAs, as is the case in other trypanosomatids, and suggest that the copy number of specific minicircle sequence classes can vary dramatically without an overall effect on the RNA editing system.

Amino Acid Sequence↗