title: Modification by preirradiation growth conditions of the shoulder of the UV fluence-survival curve of Escherichia coli B/r WP 2 thy trp and changes in mutagenic response toward tryptophan prototrophy.
abstract: The distinct three-section UV fluence-mutation frequency response (MFR) curve demonstrated in Escherichia coli strain B/r WP2 thy trp and its uvrA derivative supports the SOS hypothesis and suggests that trp+ revertants can arise either from isolated lesions (1DM) plus SOS induction or from two lesions in proximity (2DM). Preirradiation growth on arabinose instead of glucose converted the fluence-survival curve from highly shouldered to exponential but did not affect the three-section MFR curve. Prestarvation of the uvrA+ strain for tryptophan, which drastically increases the expanse of the shoulder of the survival curve, greatly decreased both 1DM and 2DM. With the uvrA strain the increase in shoulder expanse after tryptophan prestarvation was accompanied by greatly increased 2DM but no change in 1DM. Preincubation with chloramphenicol induced an even greater increase in 2DM response than amino acid prestarvation. Nalidixic acid, which prevents DNA accumulation, eliminated the response.
mesh_terms: D004307:Dose-Response Relationship, Radiation; D004926:Escherichia coli / Q000235:genetics / Q000528:radiation effects*; D009154:Mutation; D013045:Species Specificity; D014364:Tryptophan / Q000378:metabolism*; D014466:Ultraviolet Rays
chemical_list: D014364:Tryptophan