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D G MacPhee

Publications and source records attributed to D G MacPhee.

At least 73 records · Page 4Linked to original sources
PubMed1977

Spontaneous, ultraviolet and ionizing radiation mutagenesis in two auxotrophic strains of Salmonella typhimurium carrying an R plasmid.

Ultraviolet-induced, gamma-induced and spontaneous mutation yields were studied in two different auxotrophic strains of Salmonella typhimurium in the presence and absence of the UV-protecting drug resistance transfer factor R-Utrecht. One strain, carrying the hisC527 (amber) mutation, showed significantly increased spontaneous, UV- and gamma-induced mutability in the presence of the R-Utrecht plasmid. The other strain, carrying the trpD1 mutation (thought to be a missense mutation), also showed significantly increased UV mutability in the presence of the R-Utrecht plasmid. The other strain, carrying the trpD1 mutation (thought to be a missense mutation), also showed significantly increased UV mutability in the presence of the R factor, but appeared to show no significant increase in spontaneous mutability and only a very slight increase in gamma-mutability when carrying the R factor. These results demonstrate that the R-Utrecht plasmid, known to enhance UV-induced mutation yields in S. typhimurium, can also significantly enhance both spontaneous and gamma-induced mutation yields in this species. The latter effects are not so discernible with all markers, however, as shown by the results with strains carrying the trpD1 mutation. Enhancement of spontaneous mutability thus appears to be correlated with enhancement of gamma-mutability rather than UV mutability.

Gamma Rays↗
PubMed1975

Induction of base-pair substitution and frameshift mutations in wild-type and repair-deficient strains of Salmonella typhimurium by the photodynamic action of methylene blue.

Induction of back mutations to prototrophy by methylene blue (MB)-sensitized photodynamic (PD) treatment has been studied in wild-type and repair-deficient strains of Salmonella typhimurium carrying either the base-pair substitution mutation hisG46 or the frameshift mutation hisD30529 We found that reversion of the hisG46 mutation was increased in a strain carrying a uvrB deletion and decreased in a strain carrying a recA-type mutation. Reversion of the hisD3052 (frameshift) mutation, on the other hand, was decreased in both uvrB deletion and recA-type strains. The former results are consistent with the hypothesis that the majority of MB-sensitized PD-INDUCED BASE-PAIR SUBSTITUTION MUTATIONS ARIse by a mechanism similar to that currently believed to be involved in UV mutagenesis. The latter results suggest that PD-induced frameshift mutations may arise in some other way, and two possible mechanisms involving sequential action of the excision repair and recombinational repair pathways are considered.

Base Sequence↗
PubMed1975

Mutants of Salmonella typhimurium deficient in DNA polymerase I: further characterization and genetic analysis.

Tests with a plasmid-borne ochre suppressor (sup-812) and a chromosomal amber suppressor (supD501) revealed that one of three mutants of S. typhimurium deficient in DNA polymerase I was an amber mutant. Assays performed on crude extracts established that derivatives of this mutant (designated polA3) carrying ochre and amber suppressors had about 13 to 20% respectively of the enzyme activity found in the wild-type parent. The unsuppressed mutant showed less than 1% of the wild-type level of activity. Other properties of the polA3 mutant that were also partially or in some cases completely reversed by the sup-812 and supD501 suppressors included: u.v. sensitivity, methyl methanesulphonate (MMS) sensitivity, reduced ability to effect host-cell reactivation of u.v.-irradiated or MMS-treated bacteriophages, inability to maintain the (Col El) plasmid, and reduced ability to plate the phage mutant P22 c2 hpi-308. Mapping by P1-mediated transduction showed that all three polA mutations lie between metE and rha on the S. typhimurium chromosome, and that the polA mutation is cotransduced with metE at a frequency of 20% and with rha at a frequency of 8%.

Chromosome Mapping↗
PubMed1975

Mutations in Salmonella typhimurium conferring resistance to Felix O phage without loss of smooth character.

Several mutants obtained from smooth Salmonella typhimurium strains by selection for resistance to Felix O (FO) phage [whose receptor site includes the N-acetylglucosamine branch of the lipopolysaccharide (LPS) core] were smooth in cultural properties, antigenic character and phage sensitivity pattern (except for their FO resistance). However, the affected genes of several such 'FOR' (FO-resistant) mutants were shown by transduction of map in the short cysE-pyrE segment, which includes nearly all known rfa genes responsible for synthesis of LPS core. All of seven FOR mutants differed from their parents, and resembled rfa mutants with defects in the deeper part of the LPS core, by increased sensitivity to various antibiotics. One FOR mutant was non-virulent (LD50 greater than 10-7, compared with smaller than 100 for its parent); LT7 derivatives given this FOR gene by co-transduction with cysE+ were likewise non-virulent. It is inferred that FOR mutations affect the assembly of the inner part of the LPS core, perhaps causing incomplete blocks in glycosyl transferase reactions.

Acetylglucosamine↗
PubMed1971

Properties of a Salmonella typhimurium mutant with an incomplete deficiency of uridinediphosphogalactose-4-epimerase.

A galactose-negative mutant, nonleaky in respect to fermentation and utilization, isolated from a smooth Salmonella typhimurium strain by phage selection and inferred deficient of uridine diphosphate (UDP)-galactose-epimerase, was used for experiments on relation of somatic lipopolysaccharide (LPS) character to virulence. Extracts of induced mutant cells retained ca. 1% of wild-type epimerase activity and had only ca. 5% of wild-type kinase and uridyl transferase activities; also, some cultural properties of the mutant differed from those of mutants with complete defects of epimerase only. The mutant was not galactose sensitive, presumably because of its kinase defect. Although the mutant had the phage pattern (including C21-sensitivity) of an epimerase mutant, it was susceptible to transduction by phage P22 and was O-agglutinable, even when grown on defined medium; its LPS must therefore contain some O polymer, including endogenous galactose, resulting from residual epimerase activity. Growth on galactose-supplemented medium restored smooth phage sensitivity; since the mutant was partly inducible this may result, at least in part, from increased endogenous production of UDP-galactose. The mutant was made galactose positive by introduction of an F'-gal(+) plasmid. Base-change and frame-shift mutagens did not increase the frequency of reversion above the spontaneous rate. An insertion into the operator-promoter region of the gal operon seems the most likely mechanism of the mutation.

Adenine↗
PubMed1970

Recombination-deficient mutants of colicinogenic Salmonella typhimurium detected by their failure to produce colicin.

Survivors of nitrosoguanidine-treated cultures of a colicinogenic strain of Salmonella typhimurium were tested for spontaneous production of colicin E1. Of about 1,000 colonies tested, 13 produced no (or very narrow) colicin zones. Four of these isolates proved to be more sensitive to ultraviolet (UV) light, X rays, and methyl methane sulfonate than the parent strain and did not show enhanced production of colicin when treated with mitomycin C (which acts as an inducer on wild-type cells). Further studies showed that these isolates were of two classes. Three mutants were extremely sensitive to UV, failed to show spontaneous release of two temperate phages, and were infertile as recipients in transduction or in an Hfr cross although they accepted an F' factor normally. These independently isolated mutants were inferred to be recombination-deficient; one of them had the additional property of increased spontaneous mutability at two loci. The other colicin-nonreleasing isolate was only moderately sensitive to UV, showed enhanced spontaneous release of two temperate phages, and was of approximately normal fertility as a recipient in transduction or conjugation.

Colicins↗