[Effect of mutations in the relC and spoT genes of the "stringent" control regulatory system on the gene expression of Escherichia coli K-12 nucleoside catabolism].

Influence of the relC and spoT mutations on the expression of catabolite-sensitive promoters of the deo operon (cytP0 and the udp gene (udpP) was studied by defining the activity of thymidine phosphorylase (the deoA gene) and uridine phosphorylase (the udp gene) under conditions of amino acid limitation on media with different carbon sources and in the cya genome. Under certain conditions, the activity of cytP and udpP promoters increased under the action of the spoT mutation, whereas the relC mutation suppressed this effect. These findings may indicate indirectly that the ppGpp accumulation in the spoT mutant cell was responsible for the effect. However, the relC mutation itself resulted in a decrease of the activity of neither the cytP, nor the udpP. On the contrary, under certain conditions, in the cytR constitutives for thymidine phosphorylase and only in the "double" deoR cytR constitutives for uridine phosphorylase, the relC caused an increased in the cytP and udpP activity. The deoR-dependent synthesis of uridine phosphorylase was found in the relC genome, i.e. the activity of this enzyme was increased about two fold under the influence of the deoR mutation. The data obtained are explained based on the following suggestion. The ppGpp accumulation in the spoT cells, on the one hand, can activate the catabolite sensitive cytP and udpP promoters, thus promoting the Rho-dependent termination prior to these promoters (Sukhodolets, Mironov, Linkova, 1981) and, on the other hand, it can inhibit expression of catabolite sensitive promoters as a result of a possible indirect effect of lowering the level of intracellular cAMP.