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M B Coukell

Publications and source records attributed to M B Coukell.

36 records · Page 2Linked to original sources
PubMed1979

radE, a new radiation-sensitive locus in Dictyostelium discoideum.

Dictyostelium discoideum strain M28, which has been used widely in genetic studies, was found to carry a radiation-sensitive mutation. This allele, termed rad-100, was recessive in heterozygous diploids and mapped in linkage group III. Complementation analysis and survival studies on strains carrying rad-100 suggested that this allele defines a new radiation-sensitive locus in D. discoideum, and this locus has been designated radE. radE strains were moderately sensitive to ultraviolet light (D10 90 J m-2) and slightly sensitive to 137Cs gamma rays D10 255 krad). radE strains also exhibited increased sensitivity to killing by N-methyl-N'-nitro-N-nitrosoguanidine but not by other alkylating agents such as ethyl methanesulphonate or methyl methanesulphonate. The frequency of spontaneous methanol-resistant (acrA) mutants was approximately the same in cultures of radE and radE+ strains. However, when amoebae of these strains were irradiated with ultraviolet light, the frequency of induced mutants was significantly lower in cultures of the radE strain. Furthermore, when amoebae of wild-type strain NC4 were plated in the presence of caffeine after ultraviolet-irradiation, the survival curves were very similar to the curves obtained for amoebae of radE strains in the presence or in the absence of caffeine. These results suggest that the radE100 mutation and caffeine interfere with an error-prone DNA repair pathway in D. discoideum.

Alleles↗
PubMed1977

Evidence against mutational "hot-spots" at aggregation loci in Dictyostelium discoideum.

Complementation tests were performed on 10 strains of Dictyostelium discoideum which carry developmental mutations representing aggregation loci identified previously in two independent studies. When the 5 aggregation-deficient strains representing loci CGI-5 were fused with the 5 strains carrying mutations at loci ago A-E, all 25 crosses produced aggregation-competent diploids. Complicating factors, such as negative gene interactions and possible interallelic complementation are discussed. The results of this experiment suggest that the 10 aggregation loci identified in the two studies are different and that aggregation loci in D. discoideum are probably not associated with significant mutational "hot-spots".

Dictyostelium↗
PubMed1977

Linkage analysis of developmental mutations in aggregation-deficient mutants of Dictyostelium discoideum.

Simple parasexual genetic techniques have been employed to extend the linkage analysis initiated in an earlier study (Coukell, 1975) of developmental mutations (agg mutations) in 40 independently isolated aggregation-deficient mutants of Dictyostelium discoideum. Using these techniques, agg mutations in 28 of the 40 mutants have been assigned to 4 linkage groups: 16 in group II, 1 in group III, 10 in group IV, and 1 in group VI. None of the agg mutations analyzed appear to map in linkage group I. In addition, a new temperature-sensitive growth locus, designated tsgJ, was mapped in group III. It was also found that diploid strains of D. discoideum are readily induced to undergo haploidization when grown on 0.1% p-fluorophenylalanine (PFP) at 25.5 degrees C. Growth of diploid strains on PFP had no effect on the type of segregant classes obtained (i.e. PFP does not induce mitotic crossing-over), the subsequent growth and/or development of the segregants, or the ability of the segregants to reform stable diploids.

Dictyostelium↗
PubMed1975

Parasexual genetic analysis of aggregation-deficient mutants of Dictyostelium discoideum.

One hundred and thirty-nine independent, nitrosoguanidine-induced mutants blocked early in development were isolated in two haploid strains of D. discoideum. Forty of these developmental mutants were completely aggregation-deficient on bacterial lawns (Class I mutants) and these mutants were selected for parasexual genetic analysis. By fusing the Class I mutants with developmentally-competent strains the developmental mutations in 39 of these mutants were shown to be recessive; the remaining mutation appeared to be partially dominant. Complementation analysis of the developmental mutations in the Class I strains identified 5 complementation groups. Statistical analysis of the complementation data suggests that there are approximately 40 genes in this organism which will completely block aggregation when mutated and perhaps as many as 150 genes involved in some aspect of the aggregation process. Linkage analysis of 18 Class I developmental mutations revealed that 10 of these mutations map in linkage group II at a minimum of 5 loci.

Cell Aggregation↗
PubMed1971

Influence of chromosome structure on the frequency of tonB trp deletions in Escherichia coli.

The frequency of tonB trp deletions varies in different strains and substrains of Escherichia coli. Studies with chromosomal hybrids constructed by transducing various segments of the cysB-trp-suIII region from K-12(Ymel) into K-12(W3110) indicate that the characteristic low deletion frequency of K-12(Ymel) is determined largely by the (genetic) structure of the trp-suIII region of the chromosome. Transduction of the trp region from K-12(W3110) or K-12(Ymel) into strain B has little effect on the frequency of tonB trp deletions in that strain. When tonB trp deletions occur at 42 C rather than at 37 C, there is a significant reduction in the frequency of deletions in all strains examined except K-12(Ymel) and hybrids exhibiting a Ymel deletion pattern. The magnitude of this temperature effect in different K-12 strains increases proportionally with the frequency of tonB trp deletions at 37 C. At 42 C the frequency of tonB trp deletions in all K-12 strains approaches the low frequency observed for Ymel at 37 or 42 C. In contrast, spontaneous deletions in another region of the genome which simultaneously result in resistance to phages T7 and lambda and in proline auxotrophy (tfrA pro deletions) occur at a constant frequency regardless of growth temperature or the structure of the chromosome in the trp region. Two mutants of strain KB30 obtained after treatment with nitrosoguanidine show very low tonB trp deletion frequencies. The alterations in both mutants map in the trp region of the chromosome. These studies indicate that the structure of the cysB-trp-suIII region is responsible for many of the characteristic deletion frequencies observed.

Chromosome Aberrations↗
PubMed1969

Repression by glucose of acetohydroxy acid synthetase in Escherichia coli B.

Acetolactate formation in Escherichia coli B results from the activity of a single system, acetohydroxy acid synthetase, which has a pH optimum of 8.0 and is sensitive to end-product inhibition by l-valine. Acetohydroxy acid synthetase was found to be subject to catabolite repression, and the nature and concentration of the carbon source had a greater effect on the formation of the enzyme than had the known end products (valine, isoleucine, leucine and pantothenate) of the biosynthetic pathways of which this enzyme is a member. The results suggest that acetohydroxy acid synthetase may play an amphibolic role in E. coli B.

Enzyme Repression↗
PubMed1969

Relaxation of catabolite repression in streptomycin-dependent Escherichia coli.

Acetohydroxy acid synthetase, which is sensitive to catabolite repression in wild-type Escherichia coli B, was relatively resistant to this control in a streptomycin-dependent mutant. The streptomycin-dependent mutant was found to be inducible for beta-galactosidase in the presence of glucose, although repression of beta-galactosidase by glucose occurred under experimental conditions where growth of the streptomycin-dependent mutant was limited. Additional glucose-sensitive enzymes of wild-type E. coli B (citrate synthase, fumarase, aconitase and isocitrate dehydrogenase) were found to be insensitive to the carbon source in streptomycin-dependent mutants: these enzymes were formed by streptomycin-dependent E. coli B in equivalent quantities when either glucose or glycerol was the carbon source. Two enzymes, glucokinase and glucose 6-phosphate dehydrogenase, that are glucose-insensitive in wild-type E. coli B were formed in equivalent quantity on glucose or glycerol in both streptomycin-sensitive and streptomycin-dependent E. coli B. The results indicate a general decrease or relaxation of catabolite repression in the streptomycin-dependent mutant. The yield of streptomycin-dependent cells from glucose was one-third less than that of the streptomycin-sensitive strain. We conclude that the decreased efficiency of glucose utilization in streptomycin-dependent E. coli B is responsible for the relaxation of catabolite repression in this mutant.

Carbonic Anhydrases↗
PubMedDate not supplied

Regulation of expression of the cyclic nucleotide phosphodiesterase gene in phosphodiesterase inhibitor-negative mutants of Dictyostelium discoideum.

During early development of Dictyostelium discoideum, the enzyme cyclic nucleotide phosphodiesterase (PD) is produced at a low rate during the period its specific inhibitor (PDI) is being synthesized. In addition, PD gene expression is derepressed in the aggregation-deficient (Agg-), Pdi- mutant HC35. These observations suggest that the PDI might function to regulate PD gene expression, as well as modulate its activity. To explore this idea further, five new Agg-, Pdi- mutants were isolated and analyzed. All of the mutants produced high PD activity and overexpressed PD mRNA; four exhibited elevated levels of the 2400-nucleotide aggregation transcript and one overproduced the 1900-nucleotide vegetative transcript. In contrast, PD transcripts were not elevated in two Agg-, Pdi+ mutants. To determine if PDI production regulates PD expression, HC35 cells were transformed with plasmids carrying the PDI structural gene under the control of either the vegetative or aggregative PD promoter. Neither expression of PDI by the transformants nor addition of partially purified PDI to HC35 cells affected PD transcription. These results suggest that PD overexpression in the Pdi- mutants is not a direct consequence of the inability of these cells to produce inhibitor.

3',5'-Cyclic-AMP Phosphodiesterases↗