RELATIONSHIP BETWEEN SURVIVAL AND THYMINE‐DIMER EXCISION IN ULTRAVIOLET‐IRRADIATED ESCHERICHIA COLI

Abstract

Abstract— The influence of amino acid prestarvation on both the resistance to u.v. light and excision of thymine dimers of bacterial strains E. coli B/r hcr+ thy‐ trp‐, E. coli B/r hcr‐thy‐trp‐, and E, coli 15 T‐ 555–7 thy‐meth‐trp‐arg‐ has been studied. The prestarvation increased the resistance of all the strains but reasonably inhibited excision of thymine dimers. Thus the enhancement of u.v. resistance after amino acid prestarvation was not due to more complete excision of thymine dimers.

Relation Between Survival and Deoxyribonucleic Acid Replication in Ultraviolet-Irradiated Resistant and Sensitive Strains of Escherichia coli B/r

“…In both cases, the drug affected the slope and shoulder of the survival curve. We assume that acriflavine is inhibiting some mechanism other than excision repair since AA-prestarved Hcr-cells lack the ability to excise thymine dimers from their DNA (30). We also assume that the drug is not inhibiting recombination repair since its presence after irradiation (results not shown) did not increase the UV sensitivity of logarithmicphase Hcrbacteria.…”

“…We also examined the effect of inhibiting protein synthesis before irradiation on UV resistance of arabinosegrown Hcr-and Rec-E. coli B/r. Conflicting results had previously been obtained with the Hcrstrain grown on glucose (6,30).…”

“…Starvation for an essential amino acid in glucose-grown E. coli before UV irradiation (amino acid [AA I prestarvation) causes a striking increase in the size of the shoulder of the dose-survival curve (16). Current data show that AA prestarvation does not increase (1) the time available for repair prior to resumption of deoxyribonucleic acid (DNA) synthesis after UV irradiation (13) or (ii) the efficiency of the excision (30) or repair replication (29) step of excision repair.…”

Pyrimidine dimer excision in surviving and nonsurviving cells of ultraviolet-irradiated cultures of Escherichia coli

“…The increased radiation sensitivity of mutants deficient in specific types ofrepair processes (6) provides support for this hypothesis. However, survival of a culture after certain pre-and postirradiation treatments may be altered without changing the rate or extent of excision (12,17), or may be unaltered while excision is almost inhibited (13). These data are inconsistent with the hypothesis unless one assumes that repair is complete in the few viable cells and that the dimer content of the culture reflects nonviable cells.…”