[Effect of mutations for adenylate cyclase (cya) and the cyclic adenosine monophosphate receptor protein (cgp) on the gene expression of nucleoside catabolism in Escherichia coli].

The effect of cya and crp mutations on the expression of the activity of nucleoside catabolizing genes has been studied in Escherichia coli. It is found that cya and crp mutants lose their ability to grow on nucleosides as carbon sources in spite of the preservation of the basal levels of nucleoside catabolizing enzymes, found in cell-free extracts of cya and crp mutants. It is shown that cya and crp mutations completely release the influence of the regulatory gene cytR on the activity of uridine phosphorylase (udp gene) and thymidine phosphorylase (tpp gene). On this ground it is assumed that the cytR gene product acts at the level of promotors of the corresponding structural genes, causing their insensitivity to the positive action of cAMP--CRP complex. The same data concerning the effect of cya and crp mutations on cytR regulation have been reported [8], but these authors favoured the hypothesis that the cytR gene product is a repressor protein, which binds to the specific operator.