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PubMed1977

Extranuclear recombination in Aspergillus nidulans: closely-linked multiple chloramphenicol- and oligomycin-resistance loci.

A nuclear, chloramphenicol-sensitive mutant cas-1 has been isolated which is cross sensitive to a number of drugs, including oligomycin and cycloheximide. Approximately one-third of the chloramphenicol-resistant mutants isolated from mutagenized conidia of this strain were found to be extranuclear, and exhibited a variety of phenotypes. One of these mutants, designated (camB51), was slow growing on drug-free medium and recombined at low frequency with the previously described mutant (camA112) (Gunatilleke et al., 1975). The majority of extranuclear oligomycin-resistant mutants isolated from cas-1 were indistinguishable from (oliA1) (Rowlands and Turner, 1973). Two mutants, (oliB322) and (oliB332), with similar but not identical phenotypes to (oli A1), recombined with the latter at low frequency but not with each other, thus representing a new class of extranuclear mutants.

Aspergillus nidulans↗
PubMed1975

Properties of plasmids produced by recombination between R factors of groups J and FII.

Recombinant plasmids have been produced both by transduction of genetic material from FIIR factors into Proteus mirabilis strains carrying plasmids of group J and by insertion of a transposon conferring streptomycin and trimethoprim resistances into a J group R factor. The transposon-carrying derivative and one of the transductants were shown to be members of group J whereas another transductant was shown to be compatible with members of this group. This recombinant plasmid was able to eliminate but not to be eliminable by R factors of group FII. A model for the origin of this anomalous compatibility characteristic is presented based on the assumption that the recombinant plasmid carries part but not all of a complex of binding sites for the repressor of replication [Uhlin and Nordström (1975)].

Chromosome Mapping↗
PubMed1975

Physical studies of a plasmid mediating tetracycline resistance and hydrogen sulfide production in Escherichia coli.

Tetracycline resistance and hydrogen sulfide production have been previously found to be plasmid-mediated in a naturally-occurring strain of Escherichia coli; both functions are specified by a single conjugative plasmid called pIP231(Te-H2S); pIP231DNA was isolated as covalently closed molecules in dye-buoyant density gradients. The base ratio of the DNA was found to be 50% GC by density gradient analysis. Electron micrographs of plasmid molecules showed a contour length of 20 +/- 2 mum (40 +/- 4 X 10(6) daltons). Between one and two copies of pIP231 molecules per host chromosome were found in E. coli K12.

Base Sequence↗
PubMed1978

Janus green resistance in Saccharomyces cerevisiae: interaction of nuclear and cytoplasmic factors.

Janus green B was found to be a specific inhibitor of mitochondrial function in yeast. This is consistent with the Janus green specificity in supravital staining of mitochondria. A mutant of S. Cerevisiae resistant to Janus green B was isolated. It shows cross resistance to oligomycin, ethidium bromide and a weak resistance to chlormaphenicol. The mutant was found to be sensitive to cycloheximide and erythromycin. Genetic analysis of this mutant showed that mitochondrial genes are not involved in the determination of Janus Green resistance. Tetrad analysis suggested that two more more nuclear genes are concerned, but many unusal genetic features suggestive of the involvement of a cytoplasmic element remain to be explained.

Azo Compounds↗
PubMed1975

The segregation of mitochondrial genes in yeast. I. Analysis of zygote pedigrees of petite X grande crosses.

A large number of spontaneous, cytoplasmic petite mutants from six grande strains of Saccharomyces cerevisiae were crossed to a pair of isogenic tester strains. Suppressivity values were obtained by randomly sampling the diploid progeny from these crosses, and this basis, crosses were broadly categorized as having high, intermediate, or low suppressivity. For each cross, individual zygotes were obtained also. All successive first-generation buds were isolated from the zygotes, and analyzed for the presence of petite genotypes. We found that, though early buds may be mixed, all zygotes eventually produce a succession of buds which have the same genotype--either all petite or all grande. Many more zygotes from crosses in all categories of suppressivity purified to petite than expected from the population values for suppressivity. Reconstruction experiments indicate that most petite mutants may actually generate over 90% petite progeny in a petite X grande cross.

Clone Cells↗
PubMed1976

Effects of elevation of strain-ploidy on transmission and recombination of mitochondrial drug resistance genes in Saccharomyces cerevisiae.

In order to study the effects of strainploidy on the transmission and recombination of the mitochondrial genes C, E and O conferring the resistance to chloramphenicol, erythromycin and oligomycin, respectively, haploids were crossed to diploids and the results of genetic analysis were compared with those from haploid X haploid crosses. All haploid X haploid crosses showed an increased transmission of diploid derived alleles, relative to haploid derived ones, but the pattern of increase differed between homosexual and heterosexual crosses. In omega-haploid X omega-diploid homosexual crosses, the increase was of roughly equal magnitude at the C, E and O LOCI: there was a polar co-transmission of the diploid derived alleles. In omega plus haploid by omega-diploid heterosexual crosses, on the contrary, a differential increase was observed at the different loci, the magnitude being the smallest at the C locus and the largest at the O locus. As a result, there was a preferential transmission in favor of the haploid derived C alleles and of the diploid derived O alleles. A near equal transmission from both parents was observed for the E alleles. A decrease and an increase in the recombination frequency were noticed in the above haploid by diploid homosexual and heterosexual crosses, respectively. The above phenomena were ascribed to different dosages of mitochrondrial genomes from parents. Experimental data were well accorded with the theoretical expectation which were obtained on the assumptions that diploids contain twice as many mitochondrial genomes as haploids, and that random pairings and recombination would occur among mitochrondrial genomes from parents. The elevation of strain-ploidy did not affect the recombination polarity which is under the control of the omega gene. It was theoretically predicted that a preferential transmission in favor of diploid derived alleles at all the C, E and O loci would be seen in omega-haploid x omega plus diploid heterosexual crosses as well as in omega plus haploid x omega plus diploid homosexual crosses, but that the magnitude of the polar transmission would vary depending upon the loci in the former crosses, while it would be the same at all the loci in the latter ones. The recombination frequency was predicted to decrease in both of these crosses.

Chloramphenicol↗
PubMed1976

Mapping of mitochondrial genes in Saccharomyces cerevisiae. Populations and pedigree analysis of retention or loss of four genetic markers in Rho-cells.

1. Retention or loss of mitochondrial markers CR321, OR1, PR454, TR (gene loci RIB1, OLI1, PAR1, TSM1 respectively has been analysed in a large number of ethidium bromide induced primary rho-clones. Retention of one or more of the four markers with a single clone was observed frequently, only 20 to 25% of clones were found to be (TOCOOOPO). Primary clones retaining two or more of the four markers were found to be mixed, i.e. the primary rho- cell contained a heterogeneous population of variously deleted mitDNA molecules which segregated into different cell lines in the corresponding primary clone. 2. A representative sample of the population of ethidium bromide induced rho- mutants has been analysed by a first subcloning performed after some 30 cell generations of vegetative multiplication in the abscence of the drug. At this level the heterogeneous population of mitDNA molecules, generated by the mutagenic treatment in the primary cell, has been sorted out. The cells forming secondary clones are thus essentially homoplasmic. In contrast to primary clones, genotypes of secondary clones therefore could be determined unambiguously, and the frequency of cell types can be regarded as a faithful representation of the frequency of mitDNA molecules. Retention of markers was low, in less than 2% of secondary clones one or several markers have been found. This observation has been interpreted as indicating that induction of rho-mutants by ethidium bromide is accompanied by deletion of very large sequences of mitDNA in a very large fraction of mitDNA molecules. 3. Five individual rho-clones retaining the four markers TRCRORPR have been isolated and analysed for spontaneous deletion of one or several of these markers during successive subclonings (pedigree analysis). High genetic stability (98-99.5% per cell generation) has been observed in these clones. 4. A method has been developed allowing an unambiguous determination of the order of the four markers on a circular map. It is based on the concomitant loss of two markers and retention of the other two markers (double loss/double retention analysis). The results of four out of five pedigrees of individual rho-clones analysed (spontaneous deletion) and the results of the analysis of populations of secondary rho-clones (ethidium bromide induced deletion) were in full agreement and the order of genes has been determined as being P-T-C-O-P. In the fifth pedigree results suggest an inversion of the T and C markers. 5. Relative distances between pairs of markers have been derived from the frequencies of separation of markers by deletion and were found to be C-T less than C-O less than T-O less than T-P less than C-P less than O-P. Linkage of the four markers could be established, and distances calculated are additive. 6. The general relevance of this approach of mapping by deletion and the methods used for the determination of order and distances of mitochondrial genes has been discussed. (ABSTRACT TRUNCATED)

DNA, Mitochondrial↗
PubMed1977

Re-examination of F plasmid replication in a dnaC mutant of Escherichia coli.

The replication of an F' plasmid in a dnaC mutant, thermolabile for initiation of chromosomal replication, has been re-examined using a novel DNA-DNA annealing assay. Plasmid replication ceases rapidly at non-permissive conditions, consistent with a direct role for the dnaC product in the replication of F.

Conjugation, Genetic↗