Effects of alkylating agents on the induced synthesis of β-galactosidase by Escherichia coli B s−1

Abstract

The effects of alkylation by typical mono- and difunctional alkylating agents (2-chloroethyl 2′-hydroxyethyl sulphide — half sulphur mustard; and di-(2-chloroethyl)-sulphide — mustard gas) on the elementary wave of β-galactosidase synthesis induced in cells of Escherichia coli B s−1 by a brief exposure to a gratuitous inducer has been studied. The extents of alkylation of RNA, DNA and protein by these agents have been assessed by the use of [ 35S]-labelled mustards, and dose-effect relationships for the inactivation of the processes of gene transcription and mRNA translation have been obtained. It was shown that (a) the difunctional agent was no more effective in inhibiting gene transcription and mRNA translation than the monofunctional agent; (b) transcription was about five times more sensitive to alkylation than translation; (c) DNA replication in E. coli B s−1 is approximately a thousand times more sensitive to alkylation by difunctional agents than transcription, and five thousand times more sensitive than translation; (d) alkylation at successively later times during the elementary wave produced a constant depression of enzyme synthesising capacity, indicating that there is probably no specific site of attack during translation; (e) Catabolite repression appears to play no part in the inactivation of β-galactosidase synthesis by these alkylating agents. The nature and size of the target for alkylation and consequent inactivation of gene transcription and mRNA translation is discussed in the light of these results, and compared with the data obtained by other workers for inactivation by ultraviolet irradiation.