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At least 55 records · Page 3Linked to original sources
PubMed1978

Genetic recombination in Streptomyces fradiae by protoplast fusion and cell regeneration.

Conditions for highly efficient genetic recombination in Streptomyces by protoplast fusion are described. Protoplasts of S. fradiae and S. griseofuscus were formed by a modification of the glycine-lysozyme-lytic enzyme method (Okanishi, Suzuki & Umezawa, 1974). Regeneration of cells from protoplasts was monitored throughout the growth cycle and was most efficient when cells of either S. fradiae or S. griseofuscus were taken from the transition phase between the exponential and stationary growth phases. Fusion of protoplasts carrying different auxotrophic or chromosomal drug-resistance markers was achieved by treatment with polyethylene glycol, and high frequencies of stable genetic recombinants were obtained.

Polyethylene Glycols↗
PubMed1975

Genetic recombination in Nocardia mediterranei.

A system of genetic recombination in Nocardia mediterranei ATCC 13685 is described. This strain produces a mixture of several rifamycin antibiotics. Using haploid recombinant selection and analysis procedures similar to those applied to Streptomyces coelicolor A3(2), 14 auxotrophic markers and 1 streptomycin resistance marker were located on a circular linkage map. The linkage map of N. mediterranei seems to be similar to that of S. coelicolor A3(2).

Amino Acids↗
PubMed1991

[A new system of selecting yeast mutants with disrupted genetic recombination processes].

A new convenient system for isolation of the yeast mutants deficient in the genetical recombination is proposed. The chimeric plasmids constructed to carry the noncomplimenting mutant copy of the yeast ADE2 gene and different selectable yeast markers (LEU2 or TRP1 genes) are the basis for the system. Interplasmid intragenic recombination of ADE2 gene alleles in yeast cells transformed by two chimeric plasmids results in appearance of the secondary white prototrophic clones covering the primary red colony. The number of the clones reflects the recombination processes and is subject to an easy visual control. The proposed technique allows one to reveal both hypo and hyperrecombination mutants. Crossover or the gene conversion events can be distinguished by the simple genetical analysis of the secondary clones. The collection of mutants deficient in the genetical recombination has been obtained by the proposed technique.

Alleles↗
PubMed1981

Genetic analysis of the RecE pathway of genetic recombination in Escherichia coli K-12.

The RecE pathway of genetic recombination in Escherichia coli K-12 was defined to be the pathway that is utilized in deoxyribonucleic acid exonuclease V (ExoV)-defective cells which express constitutively recE+, the structural gene for deoxyribonucleic acid exonuclease VIII. Dependence on ExoVIII was shown by the occurrence in a recB21 sbcA23 strain of recombination deficiency mutations in recE, the structural gene for ExoVIII. Point mutations in recE were found as well as deletion mutations in which the entire Rac prophage, carrying recE, was lost. In addition, strain construction and mutagenesis revealed the dependence of the RecE pathway on recA+ and on recF+. Dependence on a fourth gene was shown by a mutation (rec-77) which does not map near the other genes. The problem of distinguishing the RecE pathway from that previously called RecF is discussed.

Escherichia coli↗
PubMed1985

Isolation and partial characterization of mutants of the trypanosomatid Crithidia fasciculata and their use in detecting genetic recombination.

Crithidia fasciculata was used as a model trypanosomatid to study the possible existence of genetic recombination in this group of protozoa. The approach was based on the ability to select a variety of mutants on agar plates. Following mutagenesis of wild type cells by nitrosoguanidine or ethylmethanesulfonate, stable mutant phenotypes were obtained. These included mutants resistant to the drugs actinomycin D, 6-azauracil, 6-azauridine, and 5-fluorouracil, auxotrophs and colony morphology mutants. Following mixed growth of pairs of drug-resistant mutants on selective media, isolates exhibiting stable recombinant phenotypes were obtained. The data presented suggest that 1) Crithidia undergoes some type of genetic recombination and 2) Crithidia must be diploid at some time during this process.

Amino Acids↗
PubMed1971

Genetic recombination in Streptomyces bikiniensis var. zorbonensis.

A genetic recombination system in Streptomyces bikiniensis var. zorbonensis is described. This strain produces a mixture of antibiotics including zorbamycin and zorbonomycin B and C. A genetic map has been constructed from data obtained from an analysis of haploid recombinants which shows linkage relationships of 17 marker loci. Determination of map location has been made for three different loci affecting antibiotic biosynthesis in this strain.

Amino Acids↗
PubMed1985

[The nature of genetic recombination].

The biological evolutionary axiom proposed earlier by the author states that in the absence of genetic recombination the evolution of organic forms would be impossible. In the present paper the literature data are considered, illustrating the role of genetic recombination in evolution. It is urged that a tendency towards an increasing complexity of biological organization results from periodical recombinational combining of the diverged genes as well as the whole genomes of different origin. The alternative mechanism implying the production of duplications from the identical gene copies or whole genomes is considered to be unlikely. According to the biological evolutionary axiom, the origin of life is connected with the appearance of a mode of reparation of crystalline type aggregates--the precursors of DNA by means of exchanges among their constituents. A hypothesis is proposed that in the process of recombination a certain distribution of the 6-amino bases (adenine, cytosine) along the DNA molecule is settled, with respect to the 6-carbonyl bases (guanine, thymine). It is proposed that the relative distribution of the bases mentioned influences electrostatic stability of the DNA molecule as a crystalline associate.

Animals↗
PubMed1999

Genetic recombination of poliovirus in vitro and in vivo: temperature-dependent alteration of crossover sites.

Genetic recombination that occurs with high frequency during poliovirus genome replication is a process whose molecular mechanism is poorly understood. Studies of genetic recombination in a cell-free system in vitro and in infected tissue culture cells in vivo have led to the unexpected observation that temperature strongly influences the loci at which cross-over between the two recombining RNA strands occurs. Specifically, cross-over between two genetically marked RNA strands in vitro and in vivo at 34 degrees C occurred over a wide range of the genome. In contrast, recombination in vivo at 37 and 40 degrees C yielded cross-over patterns that had shifted dramatically to a region encoding nonstructural proteins. Preferential selection of recombinants at 37 and 40 degrees C was ruled out by analyses of the growth kinetics of the recombinants. During the studies of recombination in the cell-free system we found that there is a direct correlation between the ability of a poliovirus RNA molecule to replicate in the cell-free system and its capacity to complement de novo virus synthesis programmed by another viral RNA.

Binding Sites↗
PubMed1991

Formation of Rhizobium phaseoli symbiotic plasmids by genetic recombination.

We report here the formation of symbiotic plasmids (pSyms), by genetic recombination between rearranged pSyms, which lack symbiotic information, and resistance plasmids carrying parts of different symbiotic plasmids (R's). This recombination was found to occur both between plasmids derived from different Rhizobium phaseoli isolates, and between plasmids derived from strains obtained from the same original isolate. We also present evidence on the formation of a functional symbiotic plasmid by recombination of an R', carrying nif and nod genes from strain CFN42, and an indigenous plasmid present in this strain (pCFN42e), which was thought to be unrelated to its symbiotic plasmid (pCFN42d). These data are discussed with respect to the stability and transfer of Rhizobium symbiotic information.

Drug Resistance, Microbial↗
PubMed1994

Genetic recombination between two strains of Aujeszky's disease virus at reduced multiplicity of infection.

The potential for in vivo genetic recombination has been suggested for Aujeszky's disease virus (ADV) stemming from the use of modified-live vaccines carrying vaccine-specific deletion mutations. This scenario serves as a model for the study of biological factors that affect in vivo herpesviral recombination and, ultimately, the natural evolution of herpesviruses. This report describes experiments evaluating the efficiency of ADV recombination under in vitro conditions of low multiplicity infection which were felt to represent in vivo conditions more closely than previous in vitro measurements of ADV recombination. A series of experiments were performed to measure in vitro recovery of recombinant viral progeny following co-infection of cell monolayers with non-saturating concentrations of two parental strains of ADV. A simple statistical model was generated to estimate the rate of cellular co-infection. After a single replicative cycle infectious viral progeny were recovered and their genotypes determined at two alleles by characterization of two gene loci using a battery of PCR assays. Recovery rates of parental and recombinant progeny genotypes were calculated from the PCR data. The observed frequency of recovery of recombinant viral progeny closely approximated the values projected by the model calculations. The data from our system suggest that at low multiplicity of infection, the rate of genetic recombination is a function of the probability of cellular co-infection.

Genotype↗
PubMed1987

Effects of Bloom's syndrome fibroblasts on genetic recombination and mutagenesis of herpes simplex virus type 1.

The effects of Bloom's syndrome (BS) fibroblasts on genetic recombination and the mutation frequency of herpes simplex virus type 1 (HSV-1) was determined by employing two factor crosses of selected temperature-sensitive (ts) mutants. A significant increase in the recombination frequency (RF) was observed in seven of nine crosses when multiple BS fibroblast lines were compared to normal human fibroblasts. The RF of HSV-1 ts mutants increased following 12-O-tetradecanoylphorbol-13-acetate (TPA) treatment of normal, but not BS fibroblasts, suggesting that BS fibroblasts express higher constitutive levels of genetic recombination activity. HSV-1 ts mutants demonstrated significantly higher reversion frequencies to the nontemperature sensitive (ts+) phenotype following growth in BS rather than normal fibroblasts, indicating that exogenous viral DNA encoding many of the enzymes necessary for its own replication is affected by the mutator phenotype of BS.

Bloom Syndrome↗
PubMed1988

The functional significance of DNA sequence structure in a site-specific genetic recombination reaction.

A series of sequence changes in the spacer region of the FLP recombination target (FRT) site are presented which drastically reduce site function without affecting recognition by the FLP protein. The effects follow a pattern which indicates that two structural features of the FRT site are essential for site function: a pair of pyrimidine tracts arranged in a palindrome and a predominance of AT base pairs in the spacer. The FRT site represents a sequence that serves to facilitate unwinding of the DNA within the spacer region during recombination. The results provide a clear demonstration of a role for a DNA sequence element that is distinct from protein recognition.

Bacterial Outer Membrane Proteins↗
PubMed1991

Genetic recombination in Streptomyces michiganensis DSM 40,015 revealed three genes responsible for the formation of melanin.

By UV and NTG mutagenesis numerous auxotrophic, antibiotic-resistant and melanin-negative mutants were isolated from Streptomyces michiganensis DSM 40,015 which proved to possess a efficient photoreactivation system. Using a mel- test strain with three auxotrophic markers and a antibiotic resistance for crosses with numerous prototrophic mel- strains three classes of mutants (melA, melB and melC) could be found. This classification was further supported by a series of crosses. The melC locus seemed to correspond to the melC locus of S. glaucescens which contains the tyrosinase structural gene.

Chromosome Mapping↗
PubMed1998

Genetic recombination as a reporter for screening steroid receptor agonists and antagonists.

Reporter cell lines are often used for high throughput screening of chemical libraries to identify new receptor ligands. Here we show how Cre recombinase can be used in mammalian cells to screen for steroid receptor ligands. A translational fusion of Cre recombinase and the ligand binding domain of the human glucocorticoid receptor was transfected into mammalian cells with a loxP/luciferase reporter gene. The recombinase function of the fusion is dependent on ligand binding to the receptor, and Cre-mediated recombination results in constitutive expression of luciferase from the reporter gene. A stable transfected clone was isolated and used to characterize the kinetics, ligand specificity, and dose response to various receptor ligands. The Cre fusion system, unlike a transcriptional reporter using the mouse mammary tumor virus promoter, can detect binding of the receptor antagonist RU486. We also studied the Cre reporter in a sensitive, miniaturized, assay format using an 864-well plate and show that as few as 560 cells per assay well was sufficient to measure a dose response to ligand.

Amino Acid Sequence↗
PubMed1995

Delayed onset postvaccinal mucosal disease as a result of genetic recombination between genotype 1 and genotype 2 BVDV.

Bovine viral diarrhea viruses (BVDV) are segregated into two genotypes, BVDV 1 and BVDV 2. Viruses within both genotypes may exist as one of two biotypes, cytopathic or noncytopathic. A highly fatal form of BVDV termed mucosal disease (MD) occurs when an animal persistently infected with noncytopathic BVDV becomes superinfected with cytopathic BVDV. In this study, we characterized a noncytopathic (BVDV2-125nc)/cytopathic (BVDV2-125c) viral pair isolated from an animal that died of MD 3 months after vaccination with modified-live BVDV1-NADL. In comparison to BVDV2-125nc, BVDV2-125c contained a 366-nucleotide insertion. The insertion was in the correct reading frame for the large open reading frame of the BVDV genome and occurred in the portion of the genome that codes for the p125 viral polypeptide. There was a 99% identity between the inserted sequences found in BVDV2-125c and sequences from the vaccine virus BVDV1-NADL. These data suggest that MD was induced after a recombination between noncytopathic BVD2-125nc and cytopathic vaccine virus BVDV1-NADL created the cytopathic virus BVDV2-125c.

Amino Acid Sequence↗
PubMed2001

The Whitewater Arroyo virus: natural evidence for genetic recombination among Tacaribe serocomplex viruses (family Arenaviridae).

The Tacaribe serocomplex (family Arenaviridae) comprises three phylogenetic lineages, designated A, B, and C. The sequence of a 3278-nt fragment of the small genomic segment of the Whitewater Arroyo (WWA) virus was determined to extend our knowledge on the phylogenetic relationship of this newly discovered North American Tacaribe complex virus to other arenaviruses. Independent analyses of full-length nucleoprotein (N) and glycoprotein precursor (GPC) amino acid sequences indicated that the WWA virus N and GPC genes are descended from a lineage A virus and lineage B virus, respectively. The different phylogenetic histories of the N and GPC genes indicate that the WWA virus genome is a product of recombination between two Tacaribe complex viruses.

Arenaviruses, New World↗