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R J Pinney

Publications and source records attributed to R J Pinney.

At least 55 records · Page 3Linked to original sources
PubMed1977

Preferential uptake of thymidine by thymineless enterobacteria: its significance in DNA labelling.

Minimum satisfactory concentrations of thymine and thymidine were determined for the growth of a high thymine-requirng (thy) mutant to Escherichia coli strain J5-3. Cultures were then grown in the presence of these concentrations of non-radioactive ('cold') pyrimidine together with 5 microCi/ml [methyl-3H)thymine, or [methyl-3H)thymidine (specific activities 5 Ci/m mole), and the uptake of radioactivity into ice cold trichloroacetic acid insoluble material determined. By far the most efficient labelling system was obtained if the label was supplied as radioactive thymidine and growth requirements satisfied by thymine alone. The addition of deoxyadenosine to the labelled thymidine/unlabelled thymine system dramatically reduced uptake of label. The addition of radioactive thymine with either thymine or thymidine to ensure satisfactory growth gave poor labelling. Using the [methyl-3H] thymidine/thymine system it was possible to increase the concentration of thymine from 8 to 64 microgram/ml with only a 25% reduction in label uptake after a 2 h period. The same system was also shown to be most efficient for labelling a thy derivative of another K12 strain, a thymine low-requiring (tir) K12 strain, a thy mutant of Klebsiella aerogenes 418 and a tir derivative of Salmonella typhimurium LT2.

DNA, Bacterial↗
PubMed1976

R factor-mediated resistance to ultraviolet light in strains of Escherichia coli deficient in known repair functions.

The expression of resistance to u.v. irradiation mediated by R factor R46 has been studied in strains deficient in excision repair and recombination repair. The R factor protected wild-type bacteria and also wild-type cells in which repair had been inhibited by the substitution of bromouracil for chromosomal thymine. It increased the survival of strains defective in the endonucleolytic (uvr), repolymerizing (pol) and joining (lig) stages of the excision repair process. Recombination deficient bacteria mutant at the recB or recC loci were protected by R46, but the R factor had little effect on the survival of a recA strain or a recA recB double mutant. R46 increased the survival of cells that had been treated with chloramphenicol before u.v. irradiation, but did not protect cultures treated with chloramphenciol after irradiation. It is concluded that R46 confers resistance to the lethal effects of u.v. irradiation by a mechanism that is independent of excision repair. Resistance appears to be mediated by an inducible gene product, which is possibly a nuclease and dependent on a functional host recA gene for expression.

Bromodeoxyuridine↗
PubMed1974

R-factor-mediated nuclease activity involved in thymineless elimination.

R-factor 1818 (R-1818) had no effect on the efficiency of plating of ligase-deficient phage T4 mutants on strains of Escherichia coli containing excess, normal, or defective ligase. However, if the R(+) bacterial strain that overproduced ligase was first starved of thymine, its ability to propagate ligase-deficient phage was reduced by as much as fivefold compared with the burst size on the thymine-starved R(-) strain. In contrast, it was found that after ultraviolet irradiation of the host the phage burst size was higher on the R(+) ligase overproducing strain than the R(-) derivative. The maximal level of R-factor elimination produced by thymine starvation was inversely related to the ligase level of the host. Ultraviolet irradiation did not cure the R factor from strains containing wild-type levels of ligase, but did cause elimination from strains with excess or defective ligase. The results suggest that R-1818 codes for a nuclease that is induced by thymine starvation and which, possibly in conjunction with host-mediated nucleases, is responsible for its elimination under these conditions.

Anti-Bacterial Agents↗
PubMed1973

Curing of an R factor Escherichia coli by trimethoprim.

R factor 1818, which we have shown previously to be eliminated by thymine starvation, was cured from three strains of Escherichia coli K-12 by overnight exposure to trimethoprim. Elimination was abolished in the presence of added thymine or thymidine, which suggests that curing is the result of the induction of thymineless conditions by trimethoprim. Starvation of the required amino acids proline and histidine had little effect on elimination, whereas methionine deprivation enhanced it. R factor curing was abolished by the presence of chloramphenicol, and it is concluded that protein synthesis is required for elimination to occur. It is suggested that elimination may result from the activity of a nuclease which is synthesized or induced during both direct thymine starvation and by trimethoprim treatment.

Amino Acids↗
PubMed1972

R factor elimination during thymine starvation: effects of inhibition of protein synthesis and readdition of thymine.

R factor 1818 is shown to be eliminated from a thymineless strain of Escherichia coli J6-2 (R-1818) during thymine starvation. Readdition of thymine to the starved cultures produces a partial recovery in viable count but does not affect the proportion of R(-) cells. The R factor is not cured from exponential- or stationary-phase cultures which are starved of required amino acids as well as thymine, nor from cells which are deprived of thymine in the presence of chloramphenicol. However, in both of these cases, the extent of thymineless death is reduced. It is suggested that protein synthesis is a requirement for R-1818 elimination, and the possible nature of this protein is discussed.

Amino Acids↗