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PubMed1998

[Human mitochondrial genetic system].

The mitochondria are subcellular organelles devoted to energy production in form of ATP that contain their own genetic system. Mitochondrial DNA codify a small, but extremely important, number of polypeptides of the respiratory chain. The other mitochondrial proteins are encoded in the nucleus. Therefore, mitochondrial biogenesis require the coordinated expression of nuclear and mitochondrial genetic systems. The gene arrangement in mitochondrial DNA is extremely compact with the tRNA genes interspersed with the rRNA and protein-coding genes. This organization has its precise counterpart in the mode of expression and distinctive structural features of the RNAs. Both mitochondrial DNA strands are transcribed as a whole in the form of three polycistronic molecules that are later cut by specific enzymes that recognize the 5' and 3' end of the tRNA sequences, to produced the mature rRNA, mRNA and tRNA. The mitochondrial coded mRNAs are translated into proteins by a mitochondrial specific protein-synthesizing machinery. The genetics of the mitochondrial DNA differs from that of the nuclear DNA in several features. In particular, the mitochondrial genome is inherited from the mother that transmit their mitochondrial DNA to all her offsprings. Another characteristic of this genome is its tendency to mutate more frequently than the nuclear DNA. This provides a powerful tool for studying the evolution of man.

DNA, Mitochondrial↗

PubMed2004

[The reverse genetics systems for human and animal RNA viruses].

The recovery of the virus from genetic materials in in vitro culture systems or sensitive animals is called virus rescue. A functional infectious clone of RNA virus provides unlimited possibility for genetic studies and the related reverse genetics system that allows directed genetic manipulation of an RNA virus is an extremely powerful research tool. In the past twenty years, especially since the first infectious clone of a negative-stranded RNA virus was reported in the mid-1990's, the reverse genetics systems have been available for nearly all the major human and animal RNA virus groups. The article reviews the progress of this technology, highlighting the obstacles in the construction of reverse genetics systems for major groups of human as well as animal RNA viruses and how the virologists overcame them. There are mainly four external expression systems for construction of the RNA virus reverse genetics systems basing on the kind of RNA viruses. These systems include in vitro RNA transcripts, RNA polymerase I-driven expression plasmids, RNA polymerase II-driven expression plasmids and modified vaccinia virus/T7 RNA polymerase-driven expression system. In particular, the viral nucleoprotein and polymerase proteins are required to assemble the viral ribonucleoprotein (RNP) complexes for the rescue of the negative-stranded RNA viruses. Relevant topics about the rescue of the typical viruses are discussed, including poliovirus with the de novo synthesis, Coronaviridae with the largest size of genome, Flaviviridae with the instable clones, HCV with the quasispecies nature, nodaviruses with the virus-host interaction, influenza virus with the RNA pol I transcription system, Arenavirdae with the ambisense coding strategies etc.

Animals↗

PubMed2001

Reverse genetics system for Uukuniemi virus (Bunyaviridae): RNA polymerase I-catalyzed expression of chimeric viral RNAs.

We describe here the development of a reverse genetics system for the phlebovirus Uukuniemi virus, a member of the Bunyaviridae family, by using RNA polymerase I (pol I)-mediated transcription. Complementary DNAs containing the coding sequence for either chloramphenicol acetyltransferase (CAT) or green fluorescent protein (GFP) (both in antisense orientation) were flanked by the 5'- and 3'-terminal untranslated regions of the Uukuniemi virus sense or complementary RNA derived from the medium-sized (M) RNA segment. This chimeric cDNA (pol I expression cassette) was cloned between the murine pol I promoter and terminator and the plasmid transfected into BHK-21 cells. When such cells were either superinfected with Uukuniemi virus or cotransfected with expression plasmids encoding the L (RNA polymerase), N (nucleoprotein), and NSs (nonstructural protein) viral proteins, strong CAT activity or GFP expression was observed. CAT activity was consistently stronger in cells expressing L plus N than following superinfection. No activity was seen without superinfection, nor was activity detected when either the L or N expression plasmid was omitted. Omitting NSs expression had no effect on CAT activity or GFP expression, indicating that this protein is not needed for viral RNA replication or transcription. CAT activity could be serially passaged to fresh cultures by transferring medium from CAT-expressing cells, indicating that recombinant virus containing the reporter construct had been produced. In summary, we demonstrate that the RNA pol I system, originally developed for influenza virus, which replicates in the nucleus, has strong potential for the development of an efficient reverse genetics system also for Bunyaviridae members, which replicate in the cytoplasm.

Animals↗

PubMedDate not supplied

[Comparative analysis of variability of various genetic systems in farm animals].

The particularities of the genetic structure formings of the different genetic systems (biochemical and immunogenetic markers) in the breeds, interbreed crosses of sheep and groups of cattle in connections with the locus, breed and the way of the productivity trait selections were described. The uniqueness of the characteristics and forming mechanisms of the genetic structure related with these factors and the inadequacy of the suppositions about them on the genealogical data were discussed.

Alleles↗

PubMed1991

Blood genetic systems in four Amazonian tribes.

Data on 31 genetic systems were obtained for 421 individuals belonging to the Arara, Araweté, Mundurucu, and Jamamadi tribes of northern Brazil. The Jamamadi depart farthest, and the Mundurucu least, from South American Indian averages. These data are analyzed together with those of 24 other Amazonian groups. Genetic distances and corresponding dendrograms indicate a cluster of 14 related tribes living north of the Amazon river. These genetic results show only a modest correlation with linguistic and geographic relationships among these groups.

Blood Group Antigens↗

PubMed2002

Site-specific recombination-based genetic system for reporting transient or low-level gene expression.

We report here the construction, characterization, and application of a plasmid-based genetic system that reports the expression of a target promoter by effecting an irreversible, heritable change in a bacterial cell. This system confers strong repression of the reporter gene gfp in the absence of target promoter expression and utilizes the site-specific recombination machinery of bacteriophage P22 to trigger high-level reporter gene expression in the original cell and its progeny after target gene induction. We demonstrate the effectiveness of this genetic system by tailoring it to indicate the availability of arabinose to the biological control agent Enterobacter cloacae JL1157 in culture and in the barley rhizosphere. The presence of bioavailable arabinose triggered the production of P22 excisionase and integrase from the reporter plasmid pAraLHB in JL1157, and this led to excision of the cI repressor gene, which is flanked by att sites, and the subsequent irreversible expression of gfp in the original cell and in its progeny. In culture, nearly 100% of an E. cloacae JL1157(pAraLHB) population expressed gfp after exposure to 6.5 to 65 microM arabinose for 3 h. We used this biosensor to demonstrate that arabinose was released from the seeds of several legumes and grass species during germination and from roots of barley seedlings grown hydroponically or in soil. When introduced into microcosms containing barley, the biosensor permitted the localization of arabinose along the roots. Arabinose was present near the root-seed junction and on the seminal roots but was not detected at the root tips. This recombination-based reporter system should be useful for monitoring bacterial exposure to transient or low levels of specific molecules directly in the environment.

Arabinose↗

PubMed1978

Potential of plant genetic systems for monitoring and screening mutagens.

Plants have too long been ignored as useful screening and monitoring systems of environmental mutagens. However, there are about a dozen reliable, some even unique, plant genetic systems that can increase the scope and effectiveness of chemical and physical mutagen screening and monitoring procedures. Some of these should be included in the Tier II tests. Moreover, plants are the only systems now in use as monitors of genetic effects caused by polluted atmosphere and water and by pesticides. There are several major advantages of the plant test systems which relate to their reproductive nature, easy culture and growth habits that should be considered in mutagen screening and monitoring. In addition to these advantages, the major plant test systems exhibit numerous genetic and chromosome changes for determining the effects of mutagens. Some of these have not yet been detected in other nonmammalian and mammalian test systems, but probably occur in the human organism. Plants have played major roles in various aspects of mutagenesis research, primarily in mutagen screening (detection and verification of mutagenic activity), mutagen monitoring, and determining mutagen effects and mechanisms of mutagen action. They have played lesser roles in quantification of mutagenic activity and understanding the nature of induced mutations.Mutagen monitoring with plants, especially in situ on land or in water, will help determine potential genetic hazards of air and water pollutants and protect the genetic purity of crop plants and the purity of the food supply. The Tradescantia stamen-hair system is used in a mobile laboratory for determining the genetic effects of industrial and automobile pollution in a number of sites in the U.S.A. The fern is employed for monitoring genetic effects of water pollution in the Eastern states. The maize pollen system and certain weeds have monitored genetic effects of pesticides. Several other systems that have considerable value and should be developed and more widely used in mutagen monitoring and screening, especially for in situ monitoring, are discussed. Emphasis is placed on pollen systems in which changes in pollen structure, chemistry, and chromosomes can be scored for monitoring; and screening systems which can record low levels of genetic effects as well as provide information on the nature of induced mutations. THE VALUE OF PLANT SYSTEMS FOR MONITORING AND SCREENING MUTAGENS CAN BE IMPROVED BY: greater knowledge of plant cell processes at the molecular and ultrastructural levels; relating these processes to mutagen effects and plant cell responses; improving current systems for increased sensitivity, ease of detecting genetic and chromosome changes, recording of data (including automation), and for extending the range of genetic and chromosome end points; and designing and developing new systems with the aid of previous and current botanical and genetic knowledge.

Biological Assay↗

PubMedDate not supplied

[RNA editing in different genetic systems].

One of the significant amendments to the central dogma of the molecular biology was the discovery of the RNA editing process in different genetic systems. Whereas other forms of co- and posttranscriptional modifications of messenger RNA (mRNA) (capping, polyadenilation, splicing) retain the correspondence of the primary structure of exon and final transcript, RNA editing disturbs this correspondence changing the primary structure of mRNA after its transcription. The variants of RNA-editing mechanisms are various and include site-specific insertions and deletions of one or several nucleotides (insertion-deletion editing) as well as specific modifications of nucleosides such as C-->U and A-->I deamination or U-->C transamination (conversion editing). These mechanisms differ greatly in different genetic systems but they always result in synthesis of functionally valuable proteins from "incorrect" genes and, correspondingly, can play a significant role in regulation of their expression.

Animals↗

PubMed1995

Reverse genetics system for generation of an influenza A virus mutant containing a deletion of the carboxyl-terminal residue of M2 protein.

We established a reverse genetics system for the M gene of influenza A virus, using amantadine resistance as a selection criterion. Transfection of an artificial M ribonucleoprotein complex of A/Puerto Rico/8/34 (H1N1), a naturally occurring amantadine-resistant virus, and superinfection with amantadine-sensitive A/equine/Miami/1/63 (H3N8), followed by cultivation in the presence of the drug, led to the generation of a transfectant virus with the A/Puerto Rico/8/34 (H1N1) M gene. With this system, we attempted to generate a virus containing a deletion in an M-gene product (M2 protein). Viruses lacking the carboxyl-terminal Glu of M2, but not those lacking 5 or 10 carboxyl-terminal residues, were rescued in the presence of amantadine. These findings indicate that carboxyl-terminal residues of the M2 protein play an important role in influenza virus replication. The M-gene-based reverse genetics system will allow the study of different M-gene mutations to achieve a balance between attenuation and virus replication, thus facilitating the production of live vaccine strains.

Amantadine↗

PubMed2006

Understanding mammalian genetic systems: the challenge of phenotyping in the mouse.

Understanding mammalian genetic systems is predicated on the determination of the relationship between genetic variation and phenotype. Several international programmes are under way to deliver mutations in every gene in the mouse genome. The challenge for mouse geneticists is to develop approaches that will provide comprehensive phenotype datasets for these mouse mutant libraries. Several factors are critical to success in this endeavour. It will be important to catalogue assay and environment and where possible to adopt standardised procedures for phenotyping tests along with common environmental conditions to ensure comparable datasets of phenotypes. Moreover, the scale of the task underlines the need to invest in technological development improving both the speed and cost of phenotyping platforms. In addition, it will be necessary to develop new informatics standards that capture the phenotype assay as well as other factors, genetic and environmental, that impinge upon phenotype outcome.

Animals↗

PubMed2004

Toward a new genetic system with expanded dimensions: size-expanded analogues of deoxyadenosine and thymidine.

We describe the design, preparation, and properties of two key building blocks of a size-expanded genetic system. Nucleoside analogues of the natural nucleosides dA and dT are reported in which the fusion of a benzo ring increases their size by ca. 2.4 A. The expanded dA analogue (dxA), having a tricyclic base, was first reported by Leonard nearly three decades ago. We describe a shortened and more efficient approach to this compound. The expanded dT analogue (dxT), a methylquinazolinedione C-glycoside, was previously unknown; we describe its preparation in eight steps from 5-methylanthranilic acid. The key glycoside bond formation employed Pd-mediated coupling of an aryl iodide precursor with a dihydrofuran derivative of deoxyribose. Both nucleosides are shown to be efficient fluorophores, emitting light in the blue-violet range. The base-protected phosphoramidite derivatives were prepared, and short oligonucleotides containing them were characterized. The two size-expanded nucleosides are key components of a new four-base genetic system designed to form helical paired structures having a diameter greater than that of natural DNA. Elements of the design of this expanded genetic molecule, termed xDNA, are discussed, including the possibility of up to eight base pairs of information storage capability.

DNA↗

PubMed1997

A genetic system that reports transient activation of genes in Bacillus.

Site-specific recombination is a powerful tool for precise excision of DNA fragments. We used this characteristic to construct a genetic system to report the transient activation of a promoter by promoting the stable acquisition of an antibiotic resistance marker by the bacterium. The system is composed of two compatible plasmid derivatives from Gram-positive bacteria. One of the plasmids allows the insertion of promoters upstream from tnpI, which encodes the site-specific recombinase of Tn4430. The second plasmid carries two selectable resistance genes: one is flanked by two site-specific recombination sequences and is lost following recombination; in contrast, the other resistance gene becomes functional after the site-specific recombination event. By inserting conditionally controlled promoters (the xylose-inducible xylA promoter or the plcA promoter whose expression is dependent on the growth medium) upstream of tnpI, we demonstrated that our genetic system responds to signals inducing transcription by conferring a new resistance phenotype to the host bacteria. Thus, this system can be used to identify genes which are transiently or conditionally expressed.

Artificial Gene Fusion↗

PubMed2025

Rapid Generation of Reverse Genetics Systems for Coronavirus Research and High-Throughput Antiviral Screening Using Gibson DNA Assembly.

Coronaviruses (CoVs) pose a significant threat to human health, as demonstrated by the COVID-19 pandemic. The large size of the CoV genome (around 30 kb) represents a major obstacle to the development of reverse genetics systems, which are invaluable for basic research and antiviral drug screening. In this study, we established a rapid and convenient method for generating reverse genetic systems for various CoVs using a bacterial artificial chromosome (BAC) vector and Gibson DNA assembly. Using this system, we constructed infectious cDNA clones of coronaviruses from three genera: human coronavirus 229E (HCoV-229E) of the genus Alphacoronavirus, mouse hepatitis virus A59 (MHV-59) of Betacoronavirus, and porcine deltacoronavirus (PDCoV-Haiti) of Deltacoronavirus. Since beta coronaviruses including severe acute respiratory syndrome coronavirus (SARS-CoV), severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), and Middle East respiratory syndrome coronavirus (MERS-CoV) represent major human pathogens, we modified the infectious clone of the beta coronavirus MHV-A59 by replacing its NS5a gene with a fluorescent reporter gene to create a system suitable for high-throughput drug screening. Thus, this study provides a practical and cost-effective approach to developing reverse genetics platforms for CoV research and antiviral drug screening.

Reverse Genetics↗

PubMed1977

The genetic system of kinetoplasts in trypanosomatides.

In the present report, the genetic system of Crithidia oncopelti kinetoplast is used as a model for investigation of kinetoplast DNA (kDNA) structure, its transcription, protein synthesizing apparatus of the kinetoplast and the protein synthesis controlled genetically by kDNA. It was shown that kDNA of C. oncopelti can be isolated from cells or from kinetoplast fraction in the form of a network complex structure consisting of a lot of circular molecules. These minicircles have a contour length of about 0.83 micronm and molecular weight of 1.6 X 10(6). The kDNA was demonstrated to be of higher AT content type than nuclear DNA. Besides, kDNA is characterized by a lesser degree of clustering of pyrimidines as compared with the nuclear one. The isolated kinetoplasts of C. oncopelti were shown to exhibit activity of DNA dependent RNA polymerase. The effect of some antibiotics and intercalating substances on RNA synthesis in kinetoplasts and mitochondria appears to be identical. Kinetoplasts of C. oncopelti have their own protein synthesizing system, whose components (ribosomes, rRNA, proteins, factors of incorporation) differ from those of the cytoplasm. Inhibition of translation by some antibiotics and of transcription by acriflavin allowed the suggestion that several proteins of kinetoplast ribosomes may be synthesized within this organoid. It was shown then that kDNA may be involved in the formation of the protein synthesizing apparatus in the kinetoplast.

Animals↗

PubMed1990

In vivo genetic systems in lactic acid bacteria.

A review of in vivo genetic systems covers the key features of transduction and conjugation but emphasises the intramolecular and intermolecular DNA interactions that are often associated with these processes. As well as the transfer of many lactose plasmids, conjugal transfer of nisin genes and the use of conjugation to construct bacteriophage-resistant dairy starter cultures are discussed. The discovery and characterization of insertion sequences in Lactobacillus and Lactococcus and the exploitation of heterologous conjugation and transposition systems in the lactic acid bacteria are described.

Amino Acid Sequence↗

PubMed2025

Establishment of reverse genetics systems for Colorado tick fever virus.

The Colorado tick fever virus (CTFV), which has 12-segmented double-stranded RNA genomes, is a pathogenic arbovirus that causes severe diseases in humans. However, little progress has been made in the analysis of replication mechanisms and pathogenicity. This virological constraint is due to the absence of a reverse genetics system for CTFV; therefore, we aimed to establish the system. Initially, the efficacy of CTFV replication was investigated in various cell lines. CTFV was found to grow in many cell types derived from different hosts and organs. Subsequently, BHK-T7 cells stably expressing T7 RNA polymerase were transfected with plasmids encoding each of the 12 CTFV gene segments, expression plasmids encoding all CTFV proteins, and a vaccinia virus RNA-capping enzyme. Following transfection, the cells were co-cultured with Vero or HeLa cells. Using this system, we rescued monoreassortants and recombinant viruses harboring peptide-tagged viral proteins. Furthermore, an improved system using Expi293F cells expressing T7 RNA polymerase was established, which enabled the generation of recombinant reporter CTFVs. In conclusion, these reverse genetics systems for CTFV will greatly contribute to the understanding of viral replication mechanisms, pathogenesis, and transmission, ultimately facilitating the development of rational treatments and candidate vaccines.

Animals↗

PubMed2001

Reverse genetics system for the avian coronavirus infectious bronchitis virus.

Major advances in the study of the molecular biology of RNA viruses have resulted from the ability to generate and manipulate full-length genomic cDNAs of the viral genomes with the subsequent synthesis of infectious RNA for the generation of recombinant viruses. Coronaviruses have the largest RNA virus genomes and, together with genetic instability of some cDNA sequences in Escherichia coli, this has hampered the generation of a reverse-genetics system for this group of viruses. In this report, we describe the assembly of a full-length cDNA from the positive-sense genomic RNA of the avian coronavirus, infectious bronchitis virus (IBV), an important poultry pathogen. The IBV genomic cDNA was assembled immediately downstream of a T7 RNA polymerase promoter by in vitro ligation and cloned directly into the vaccinia virus genome. Infectious IBV RNA was generated in situ after the transfection of restricted recombinant vaccinia virus DNA into primary chick kidney cells previously infected with a recombinant fowlpox virus expressing T7 RNA polymerase. Recombinant IBV, containing two marker mutations, was recovered from the transfected cells. These results describe a reverse-genetics system for studying the molecular biology of IBV and establish a paradigm for generating genetically defined vaccines for IBV.

Animals↗

PubMed1994

Partial outlet obstruction of the rabbit bladder results in changes in the mitochondrial genetic system.

In the rabbit, partial outlet obstruction of the urinary bladder results in significant changes in the physiology, cellular structure, and cellular metabolism of that organ. One of the most striking changes observed is a 50% decrease in oxidative metabolism. Here we investigate whether the function of the mitochondrial (mt) genetic system is altered in rabbit bladder tissue following partial outlet obstruction. Southern analyses of total DNA prepared from bladder tissue excised as a function of time after initiation of partial outlet obstruction showed that the relative number of copies of the mt genome decreases as much as 10-fold during the first 7 d after obstruction, and that this attenuated mt genome copy number is maintained until at least 14 d post-obstruction. Northern analyses, in contrast, showed that mt COII and cytochrome b transcript levels initially decrease but recover to control levels by about 5 d after obstruction; that level is maintained through 14 d post-obstruction. Enzymatic analysis of cytochrome oxidase and NADH cytochrome c reductase activities in obstructed bladder tissue gave results which paralleled the pattern in the mt RNA analyses. Surprisingly, transcript levels for the mt-related nuclear COIV gene rapidly decreased to about 50% of control levels following obstruction and remained there until 14 d post-obstruction. These results indicate that partial outlet obstruction of the rabbit bladder leads to significant changes in the status and expression of the mt genetic system in bladder tissue.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗