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PubMed2025

Genomic evolution of EGF-CFC genes in deuterostomes.

BACKGROUND: EGF-CFC proteins are a bilaterian innovation, but they are best known for their roles in Nodal signaling during gastrulation and left-right patterning in vertebrates. Species with multiple family members show evidence of functional specialization. For example, in mouse, Cripto is required for gastrulation, whereas CFC1 is involved in left-right patterning. However, members of the EGF-CFC family across model organisms exhibit limited sequence conservation beyond the EGF-CFC domain, posing challenges for determining their evolutionary history and functional conservation. RESULTS: In this study, we describe the evolutionary history of the EGF-CFC family of proteins across several branches of deuterostomes, with a particular focus on vertebrates. We trace the EGF-CFC gene family from a single gene in the deuterostome ancestor through its expansion and functional specialization in tetrapods, and subsequent gene loss and translocation in eutherian mammals. Mouse Cripto and CFC1, zebrafish Tdgf1, and each Xenopus EGF-CFC gene (Tdgf1, Tdgf1.2 and Cripto.3) are all descendants of the ancestral deuterostome Tdgf1 gene. CONCLUSIONS: We propose that subsequent to EGF-CFC family expansion in tetrapods, Tdgf1B (Xenopus Tdgf1.2) acquired specialization in the left-right patterning cascade, and then after its translocation in eutherians to a different chromosomal location, CFC1 has maintained that specialization.

Animals↗

PubMed1992

Multiple autoepitope presentation for specific detection of antibodies in primary biliary cirrhosis.

Antimitochondrial autoantibodies are present in sera from close to 95% of patients with primary biliary cirrhosis. The so-called primary biliary cirrhosis-specific antigen, named M2, was found to be associated with an enzyme complex of the inner mitochondrial membrane and, more precisely, with the E2 component, dihydrolipoamide acetyltransferase, of the pyruvate dehydrogenase complex. We recently established that an immunodominant epitope recognized in direct enzyme-linked immunosorbent assay by primary biliary cirrhosis M2+ sera, but not by non-primary biliary cirrhosis M2+ sera, could be mimicked by a synthetic peptide encompassing residues 167-184 of the E2 component and associated with lipoic acid. This fragment is present in the natural inner lipoyl-binding site of the human enzyme, and the presence of lipoic acid located on lysine 173 was found to be essential to allow IgG antibody binding. In this study we have improved the enzyme-linked immunosorbent assay test based on the synthetic peptide-lipoic acid conjugate by using a multiple antigen peptide system containing eight copies of the peptide as antigen. This approach avoids the use of a peptide conjugated to a carrier protein and was found to be particularly efficient because 23 of 27 primary biliary cirrhosis M2+ sera (85%) could be identified. A multiple antigen peptide without lipoic acid was not recognized by primary biliary cirrhosis antibodies. The peptide used in the multiple antigen peptide construction was a short 13-mer peptide encompassing a highly conserved sequence present in both the outer (residues 40-52) and the inner (residues 167-179) lipoyl-binding sites of the enzyme.(ABSTRACT TRUNCATED AT 250 WORDS)

Acetyltransferases↗

PubMed1979

Molecular structure and flanking nucleotide sequences of the natural chicken ovomucoid gene.

Five independent clones containing the natural chicken ovomucoid gene have been isolated from a chicken gene library. One of these clones, CL21, contains the complete ovomucoid gene and includes more than 3 kb of DNA sequences flanking both termini of the gene. Restriction endonuclease mapping, electron microscopy and direct DNA sequencing analyses of this clone have revealed that the ovomucoid gene is 5.6 kb long and codes for a messenger RNA of 821 nucleotides. The structural gene sequence coding Ifor the mature messenger RNA is split into at least eight segments by a minimum of seven intervening sequences of various sizes. The shortest structural gene segment is only 20 nucleotides long. All seven intervening sequences are located within the peptide coding region of the gene, and the sequences at the 5' and 3' untranslated regions of the mRNA are not interrupted by intervening sequences. The DNA sequences of the regions flanking the 5' and 3' termini of the gene have been determined. Thirty nucleotides before the start of the messenger RNA coding sequence is the heptanucleotide TATATAT, which is also present in a similar location relative to the chicken ovalbumin gene and other unique sequence eucaryotic genes. This sequence resembles that of the Pribnow box in procaryotic genes where a promoter function has been implicated. Seven nucleotides past the 3' end of the gene is the tetranucleotide TTGT, a sequence found to be present at identical locations as either TTTT or TTGT in other eucaryotic genes that have been sequenced. These conserved DNA sequences flanking eucaryotic genes may serve some regulator function in the expression of these genes.

Animals↗

PubMed2026

Mutation rate heterogeneity biases variant effect prediction and reveals genuine mutational robustness.

Variant effect predictors (VEPs) are widely used to interpret the functional consequences of human genetic variation. Because most methods rely on sequence conservation, they implicitly treat conservation as evidence of functional constraint. However, substitution patterns across a phylogeny reflect not only selection but also differences in underlying mutation rates. Here, we show that this creates a systematic confounding: most VEPs capture mutation rate variation and misinterpret it as variation in functional importance. Widely used conservation metrics exhibit a related bias; in particular, phyloP scores correlate strongly with mutation rate even at putatively neutral sites. Consequently, variants at low-mutation-rate sites tend to be predicted as more damaging, and variants at highly mutable sites as more tolerated, than warranted by their true functional impact. We also identify a distinct biological signal in experimental measurements of mutational effects on protein stability: amino acid substitutions that are more likely to arise are, on average, less destabilizing than rarer substitutions. This provides empirical support for mutational robustness in the context of protein stability. However, this relationship is insufficient to explain the mutation-rate dependence observed in current VEP outputs. Together, our findings show that mutation rate heterogeneity systematically biases current variant effect prediction frameworks, highlight the need to model mutation probabilities explicitly in future VEPs, and reveal a genuine biological signal of mutational robustness.

conservation scores↗

PubMed2026

Melioribacter sulfuriphilus sp. nov., facultatively anaerobic thermophilic sulfur- and thiosulfate-respiring bacterium from Karmadon hot springs of North Ossetia (Russian Federation).

Novel facultatively anaerobic moderately thermophilic bacteria, strains OK-6-MeT and OK-1-Me, were isolated from the hot springs of Karmadon (North Ossetia, Russian Federation). Gram-stain-negative, motile rods were present singly, in rosettes, and formed biofilms. Both strains grew optimally at 55 °C, pH 7.0 and did not require sodium chloride. They were chemoorganoheterotrophs, growing on mono-, di- and polysaccharides (cellulose, xylan, lichenan, xyloglucan, mannan, locust bean gum, pectin) as well as proteinaceous substrates (gelatin, casein). Growth under anaerobic conditions was observed both in the presence and absence of external electron acceptors (sulfur, thiosulfate, nitrite, arsenate, Fe-citrate, ferrihydrite). Major cellular fatty acids of both strains were iso-C15:0, anteiso-C15:0, and anteiso-C17:0. The size of the genomes were 3.3 and 3.2 Mb for strain OK-6-MeT and OK-1-Me, respectively. Genomic DNA G + C content was 37% for both strains. According to the 16S rRNA gene sequence and conserved protein sequences phylogenies, the strains represented a new species of the genus Melioribacter of family Melioribacteraceae within the class Ignavibacteria, for which the name Melioribacter sulfuriphilus sp. nov. is proposed, with type strain OK-6-MeT (= B-3972T = CGMCC 1.18264 T = BIM B-2154T = UQM 41932T). Analysis of OK-1 and OK-6 metagenomes revealed presence of various genes involved in carbon (CO2 fixation, carbohydrate hydrolysis, hydrocarbons degradation, fermentation), nitrogen (nitrate, nitrite, NO and N2O reduction) and sulfur cycles (sulfate reduction, sulfur or thiosulfate reduction, oxidation of sulfur compounds). MAGs OK-1-035 and OK-6-024 almost identical to genomes of strain OK-1-Me and OK-6-MeT presumably are integral part of these complex trophic chains.

Facultative anaerobe↗

PubMed2026

Proteolytic activation of c-MYC facilitated by DOT1L.

c-MYC is a key regulator of growth and metabolism. Functional and molecular cooperation between the H3K79 methyltransferase DOT1L and c-MYC has been reported in several human cancer types, but the nature of their interaction remains undefined. We demonstrate that DOT1L and MYC [Myc and Mondo-like (MML-1) in Caenorhabditis elegans] coregulate genes in the nematode model and mammalian cancer cells. Moreover, both c-MYC and MML-1 exhibit cleavage products facilitated by DOT1L function. Surprisingly, we found a similarity between a conserved sequence in DOT1 proteins and the DDI-family protease catalytic motif. We characterize a c-MYC sequence preceding the DNA-binding domain as a site of nuclear proteolytic cleavage, demonstrate its importance for transcription activation by c-MYC, and propose that c-MYC is activated by a protease, as previously reported for Nuclear factor erythroid 2-related factor (NRF) and SREBP transcription factors. Our results suggest that DOT1L may activate c-MYC and other transcription factors in the nucleus by acting as a protease.

Animals↗

PubMed2025

Origin and Evolution of Bacterial Periplasmic Force Transducers.

In double-membraned bacteria, non-equilibrium processes that occur at the outer membrane are typically coupled to the chemiosmotically energized inner membrane. TolA and TonB are homologous proteins which energetically couple inner membrane motor proteins to the essential processes of outer membrane stabilization and substrate import, respectively. The evolutionary trajectories of these proteins have been difficult to elucidate due to low-sequence conservation, yet they are thought to transduce force similarly. Here, this problem was addressed using structural prediction approaches to identify and annotate force transduction operons to trace their distribution and evolutionary origins. In the process, we identify a novel outer membrane-tethering system and a previously unknown family of monomeric force transducers. This approach revealed putative tolA genes, and thus the core organizational principles of the tol-pal operon throughout diverse bacterial taxa. We discovered that the α-helical structure of the periplasm-spanning domain II of TolA previously thought its hallmark, is anomalous amongst most Tol-Pal systems. This structure is mainly prevalent in γ-proteobacteria, likely in adaptation to their lifestyle. Comparison of Tol-Pal and Ton system distribution suggests that TolA emerged from a TonB paralogue and co-emerged with Pal, the outer membrane-tethering lipoprotein that functionalizes the Tol-Pal system. We also determined that TolB, the Pal-mobilizing protein, likely emerged from a family of outer membrane proteins; and CpoB, a periplasmic factor that coordinates peptidoglycan remodeling with cell division, was originally a lipoprotein present in the ancestral Tol-Pal system. The extensive conservation of the Tol-Pal system throughout Gracilicutes highlights its significance in bacterial cell biology.

Evolution, Molecular↗

PubMed2025

Interstrain Recombinants of Human Cytomegalovirus Reveal Complex Genetic Correlates and Epistasis Influencing Glycoprotein Display, Virion Infectivity and Spread Characteristics.

Most of the nucleotide diversity in the human cytomegalovirus (HCMV) genome is due to approximately 17 genes with 2-14 alleles each. These allelic genes are interspersed among longer stretches of highly conserved sequences with signatures of extensive recombination that would shuffle the allelic genes into a vast number of allelic haplotypes. Bacterial artificial chromosome clones derived from 3 independent clinical isolates (TB40/e (TB), TR and Merlin (ME)) display dramatic differences in the abundance of entry-mediating glycoproteins gH/gL/gO and gH/gL/UL128-131, virion infectivity and efficiency of cell-free and cell-to-cell modes of spread. Of these, TB and ME are the most phenotypically different and share only 2 of the 17 allelic genes. A set of recombinant HCMV was generated by coinfecting cells with TB and ME and restriction fragment length polymorphism (RFLP) analyses demonstrated complex crossover patterns. Most recombinants were either "TB-like" with much more gH/gL/gO than gH/gL/UL128-131, or "ME-like" with much more gH/gL/UL128-131. This correlated with a TB or ME UL128 sequence, consistent with a G/T polymorphism affecting UL128 pre-mRNA splicing. One recombinant had a gH/gL/gO:gH/gL/UL128-131 ratio of 0.8, suggesting genetic determinants beyond UL128. Virion infectivity correlated with TB versus ME-like glycoprotein display, but intragroup variability indicated additional factors and variability in spread efficiency and the contribution of cell-free and cell-to-cell spread modes indicated an influence of characteristics beyond virion infectivity. Results suggest that the relationships among these three phenotypes are not strictly causal and that all three phenotypes are genetically complex and influenced by epistasis among polymorphic loci across the genome.

Journal Article↗

PubMed2025

Genome-wide diversity of chromosomal inversions and their disease relationships.

Chromosomal inversions shape evolution and are implicated in human disease, yet their effects on genomic variation and health outcomes remain poorly understood. We analyze genome-wide human inversion polymorphisms, contrasting single-event and recurrent loci. Inversion recurrence is validated using structured-coalescent simulations. We show that single-event inversions evolve in near-complete isolation: inverted haplotypes show ~16-fold lower diversity and strong differentiation from direct haplotypes (median FST = 0.33). By contrast, recurrent inversions maintain gene flow, resulting in similar diversity across orientations and ~4-fold lower differentiation. We further find marked differences in coding sequence conservation between single-event and recurrent inversions. Using the NIH All of Us biobank, we impute inversions and identify four inversions with significant disease associations. Notably, the 17q21 inversion is associated with reduced risk of cognitive decline (OR=0.919) and breast cancer (OR=0.910) but with increased obesity risk (OR=1.097), consistent with pleiotropic selection. These findings establish inversions as major drivers of human genetic diversity and disease, with evolutionary outcomes critically dependent on recurrence.

Evolution↗

PubMedDate not supplied

Functional analysis of the promoter of a sea urchin metallothionein gene.

The 5'-flanking region of the metallothionein (MT) gene LpMT1 of the sea urchin Lytechinus pictus includes three copies of a conserved sequence that includes the metal-responsive element (MRE) consensus core sequence required for heavy metal induction of other MT genes, a GC box, a G box of a putative basal level enhancer element which includes another MRE core element, and a poly(C) tract. A fragment of LpMT1 DNA from nucleotides +31 to -309 fused to a chloramphenicol acetyltransferase reporter gene was inducible with cadmium after injection into L. pictus embryos. This induced activity was greatly reduced in a deletion mutant which retained only 195 base pairs of 5'-flanking sequence, including the proximal pair of MREs and the G box, but excluding the poly(C) tract, GC box, and distal MRE. A potent human hMT-IIA gene promoter is marginally functional in L. pictus embryos. In contrast, the LpMT1 promoter is active in HeLa cells and in embryos of the sea urchin Strongylocentrotus purpuratus. The hMT-IIA gene may lack a cis-acting sequence element required for expression of MT genes in L. pictus embryos. The LpMT1 promoter is a powerful, inducible, promiscuous promoter useful for driving the expression of heterologous genes in sea urchin embryos.

Animals↗

PubMed2025

An interbacterial cysteine protease toxin inhibits cell growth by targeting type II DNA topoisomerases GyrB and ParE.

Bacteria deploy a diverse arsenal of toxic effectors to antagonize competitors, profoundly influencing the composition of microbial communities. Previous studies have identified an interbacterial toxin predicted to exhibit proteolytic activity that is broadly distributed among gram-negative bacteria. However, the precise mechanism of intoxication remains unresolved. Here, we demonstrate that one such protease toxin from Escherichia coli, Cpe1, disrupts DNA replication and chromosome segregation by cleaving conserved sequences within the ATPase domain of type II DNA topoisomerases GyrB and ParE. This cleavage effectively inhibits topoisomerase-mediated relaxation of supercoiled DNA, resulting in impaired bacterial growth. Cpe1 belongs to the papain-like cysteine protease family and is associated with toxin delivery pathways, including the type VI secretion system and contact-dependent growth inhibition. The structure of Cpe1 in complex with its immunity protein reveals a neutralization mechanism involving competitive substrate binding rather than active site occlusion, distinguishing it from previously characterized effector-immunity pairs. Our findings unveil a unique mode of interbacterial intoxication and provide insights into how bacteria protect themselves from self-poisoning by protease toxins.

Escherichia coli↗

PubMed2026

Deep DNA and protein level feature integration for robust clinical variant interpretation using probabilistic gradient boosting.

A major challenge in clinical genomics is to classify genetic variations correctly, since it directly affects disease diagnosis and personal care. The existing methods tend to be based on the combination of different factors, such as protein structure, population frequencies, phenotypic annotations, and sequence conservation. Nevertheless, these methods often cannot be used to achieve the necessary interpretability, quantify uncertainty, and address rare cases. This paper presents a probabilistic gradient boosting model on variant pathogenicity prediction. The suggested framework applies biological characteristics at both level of DNA and protein levels while also scaling the level of uncertainty in clinical decision making. Our machine learning aims to solve the issues of variant interpretation by managing the features and through probability-based pathogenicity prediction. The framework formulation is aimed at generalizing over various datasets and minimizing overfitting. At the same time, it can ensure reasonable performance to facilitate clinical experiments. The model has also been tested on three standard datasets and demonstrated to be more predictive of the pathogenic effect of variants, in comparison with a variety of existing tools. The probabilistic gradient boosting model proposed had ROC AUC values of 0.9293, 0.9610, and 0.9646 on ClinVar variants, GRCh37, and GRCh38 human genome respectively. Furthermore, the dataset was ensured to include both exonic and intronic variants, and Variants of Uncertain Significance were also taken into consideration for Performance Testing. Through this it also aims to provide better clinical significance which will lead to a good interpretable tool for priority of variants for a large variety of disease conditions.

ClinVar↗

PubMed2026

Proteome-wide curation of experimentally validated HPV T-cell epitopes identifies key gaps in our understanding of cellular immunity to HPV and informs vaccine design.

BACKGROUND: Human papillomavirus (HPV) drives both malignant and benign tumours. Current prophylactic vaccines are type-restricted, not optimised for T-cell induction, and lack therapeutic efficacy. Although T-cells are critical for both preventing and clearing HPV infection, experimentally validated HPV T-cell epitopes remain fragmented across the literature, limiting systematic evaluation of cellular immune targets. METHODS: We curated experimentally validated HPV T-cell epitopes from the Immune Epitope Database (IEDB). Epitopes were mapped across HPV proteins and genotypes, and analysed for response rate, sequence conservation across 454 representative HPV genomes, and HLA restriction patterns. RESULTS: 485 unique experimentally validated HPV epitopes have been described (133 studies; 1,494 functional assays). Consistent with research focus and viral biology, E6 and E7 proteins account for >60% of known HPV epitopes despite accounting for ~10% of the viral proteome. High-risk HPV types, especially HPV16 and HPV18, were the most studied (p <.001) and were enriched for CD8+ epitopes (p <.001). We identified major knowledge gaps, including: underrepresentation of structural proteins such as L2; limited epitope coverage for low-prevalence HPV genotypes; a bias towards common HLA alleles. In silico analysis indicated greater conservation of epitopes in L1/L2 and across high-risk HPV types. Conserved, commonly detected, and HLA-promiscuous epitopes were highlighted and we provide panels of candidate epitopes for consideration in immune monitoring, broad-spectrum prophylactic vaccines, and high-risk targeted therapeutic vaccines. CONCLUSION: This study provides the first comprehensive atlas of experimentally validated HPV T-cell epitopes and ranked epitope candidates for translational application. We demonstrate that our understanding of HPV T-cell immunity is constrained by biases in antigen, genotype and HLA focus and by incomplete epitope mapping. Addressing these gaps will be essential for a comprehensive assessment of cellular immunity and for utilising T-cells in next-generation vaccines.

Epitopes, T-Lymphocyte↗

PubMed2026

Tobamoviruses: Advances in Molecular Biology, Host Interactions and Integrated Disease Management.

Tobamoviruses (viruses in the genus Tobamovirus, family Virgaviridae) lead to major yield losses in economically important crops around the world. In this review, we go beyond the canonical gene expression framework by integrating recent discoveries of reverse open reading frames (rORFs) on the negative-strand RNA. These rORFs have only been experimentally validated in cucumber green mottle mosaic virus (CGMMV), with predicted sequence-conserved homologs across a subset of the genus, including TMV, ToBRFV, and PMMoV. However, they are not universally present in all tobamoviruses. We systematically dissect the infection cycle-from disassembly and replication to cell-to-cell and systemic movement-with an emphasis on the host factors hijacked at each stage. We synthesize current understanding of plant antiviral immunity, focusing on RNA silencing and NLR receptor-mediated resistance as two pillars of defense, along with the transcription factors and microRNAs that orchestrate these responses. We critically evaluate the experimental evidence for both plant defenses and viral counter-strategies, noting that many mechanistic models derive from limited model systems. We further characterize host genetic resistance and susceptibility factors applicable to crop breeding. These resources include dominant NLR and non-NLR resistance, as well as recessive resistance derived from modified host susceptibility genes. We address how viral mutations, recombination and fitness trade-offs undermine resistance durability. We then evaluate their practical deployment through conventional breeding, the exploitation of quantitative resistance, and genome editing, and outline associated agronomic drawbacks and regulatory constraints. Using ToBRFV as a case study, we analyze its epidemiological traits and assess the current arsenal of surveillance tools, from field diagnostics to remote sensing. Finally, we survey management strategies across a spectrum of maturity. Some approaches, including sanitation protocols and conventionally bred resistant cultivars, have proven effective under field conditions. The first dsRNA-based biopesticide has recently been registered in China, while other biological control agents and low-risk chemical approaches remain largely at the experimental stage. We also discuss the bottlenecks that impede lab-to-field transition and highlight promising solutions such as precision breeding and evolution-oriented cultivar deployment. By bridging molecular virology, epidemiology, and integrated disease management, this review provides a critical, bench-to-field framework for the sustainable control of tobamoviruses.

TMV↗

PubMed1992

Population genetics of rheumatoid arthritis.

A major component of genetic susceptibility to rheumatoid arthritis (RA) appears to be explained by inheritance of HLA-DRB1 alleles, which have a conserved sequence of amino acids in the third hyper-variable region of the molecule. This "shared epitope" is found on various DR4, DR1, and DR6 variants, as well as on DR10. The evidence for this "shared epitope" in RA is examined at the population level, including how it fits in with the available epidemiologic data and RA disease severity.

Alleles↗

PubMed1992

[RNA editing].

Explore the source record for details and available documents.

Animals↗

PubMed2026

Bridging the gap between legacy polymerase chain reaction-based microsatellite data with high-throughput sequencing data for conservation genomics.

Microsatellites are powerful markers for tracking genetic variation in wildlife populations due to their high polymorphism and genome-wide abundance. While polymerase chain reaction (PCR)-based fragment size analysis has been the standard for genotyping microsatellites, high-throughput sequencing offers greater resolution and the opportunity to sync historical datasets with modern analyses. We evaluated how genotypes from whole-genome sequencing align with PCR data for 15 microsatellite loci in 11 North American brown bears (Ursus arctos). Brown bear populations in the 48 contiguous United States have declined from approximately 50,000 to fewer than 2,000 over the past decades. Their endangered status has prompted extensive research and genetic monitoring, yielding large, multiyear microsatellite datasets upon which future conservation efforts can build. We achieved an overall microsatellite genotype concordance rate of 94.5% comparing high-throughput sequencing results to PCR based-fragment size results. All discrepancies occurred at complex loci containing multiple insertions and/or deletions (indels). Physically linked indels or single nucleotide polymorphisms (SNPs) occurring within the loci were misinterpreted as independent insertions, underscoring the need for genotyping tools that incorporate phasing when genotyping. To evaluate coverage effects, we downsampled high-throughput sequence data from 30x to 2x. Concordance remained high at 20 to 30x but dropped sharply at 10x, with 5x and 2x having discordant genotypes or insufficient coverage for genotyping. Accurate genotyping required both sufficient depth and number of reads spanning the entire repeat regions. Our results show that short-read whole-genome sequencing can recover microsatellite genotypes with high accuracy when paired with careful variant interpretation. By aligning historical PCR datasets with modern sequencing data, we can preserve decades of genetic insight and strengthen long-term monitoring of at-risk populations.

Animals↗

PubMed1978

Conservation of the sequence and position of the ribosomal RNA genes in Tetrahymena pyriformis mitochondrial DNA.

1. We have done cross-hybridizations between the mitochondrial ribosomal RNAs and DNAs from strains ST and PP of Tetrahymena pyriformis. DNA . ribosomal RNA hybrid formation can be completely prevented by an excess of the heterologous ribosomal RNA and the heterologous hybrids melt 6 degrees C below the homologous hybrids. This shows that the ribosomal RNA cistrons can account for the 5% cross-hybridization previously observed between the mtDNAs of strains PP and ST (Goldbach et al. (1977) Biochim. Biophys. Acta 477, 37--50). 2. By electron microscopy of DNA . ribosomal RNA hybrids we have determined the position of the ribosomal RNA cistrons on the mtDNA of strain GL, a mtDNA which we have shown to contain a sub-terminal 1 micron duplication-inversion and a terminal palindrome at one end which varies in length from 0 to 5 micron and which includes the 1 micron duplication-inversion (Arnberg et al. (1977) Biochim. Biophys. Acta 477, 51--69). The 21 S ribosomal RNA cistron overlaps the 1 micron duplication-inversion and as a result two or three cistrons are present, depending on the size of the terminal palindrome. Only one 14 S ribosomal RNA cistron is found, located about 10 000 base pairs away from the nearest 21 S cistron is found, located about 10 000 base pairs away from the nearest 21 S cistron and with the same polarity as this cistron. 3. We conclude from these results and those in the preceding paper that the sequence of the ribosomal RNAs and the position of the ribosomal RNA genes in the mtDNA is strongly conserved in Tetrahymena. Possible reasons for the duplication of 21-S ribosomal RNA genes and the terminal heterogeneity of Tetrahymena mtDNA are discussed.

Animals↗