Studies on Mutations Induced by Nonlethal Dosages of Ultraviolet Light

The dose range of nonlethal but mutagenic ultraviolet light was delineated for the streptomycin-resistance locus (loci) in E. coli B/r. The nonlethal system described is urique in its response to nutrition during the period of phenotypic expression and in the time required for fixation or stsbilization of the mutant factor(s). No nutritional response occurs when the streptomycin-resistaat mutants are induced by dossges of ultraviolet that are lethal to a large portion of the population. Preliminary investigations with chloramphenicol indicate that both protein synthesis and synthesis of other nuclear components are required for the fixation and expression of part of the induced mutations. Preliminary work with metabolite analogs suggests the possibility that the numbers of mutants to be expressed may be increased or decreased by use of the appropriate analog. Ultraviolet light is postulated to have two mechanisms of action: It produces, perhaps by direct effect, mutants which are not modified by postirradiation nutrition, and, in addition, it produces mutants which are subject to modification by appropriate postirradiation treatment. Presumably the latter are due to an indirect effect of the irradiation. (auth)