THE EFFECT OF POSTTREATMENT WITH OHLORAMPHENICOL VARIOUS ULTRAVIOLET-INDUCED MUTATIONS IN ESCHERICHIA COLI

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Abstract
The effect of posttreatment with chloramphenicol and/or amino acid deprivation on the frequency of UV-induced mutations to streptomycin resistance, streptomycin independence, and ability to ferment lactose was investigated, using strains derived from E. coli B/r. The yield of mutations from lac to lac+ was markedly and irreversibly reduced by the posttreatment, but there was no appreciable effect on mutations to str-r and stri-i. It was concluded that mutations to the ability to ferment lactose, like most mutations to prototrophy, are established only if conditions Ifavor the synthesis of proteins during the postirradiation "sensitive period, " but that mutations to streptomycin resistance and streptomycin iridepend-ence have no such requirement. Two distinct pathways of mutagenesis initiated by ultraviolet light are inferred.