[Disturbance of the tandem promotor functioning of the Escherichia coli K-12 deo-operon in the genome of the rho15(ts) mutant for the transcription termination factor].

The effect of the rho15(ts) mutation on the expression of Escherichia coli deo operon's genes is studied. In relation to the regulatory deoR and cytR genes, the rho15 mutation causes in wild type genome 2,5-fold increase in both thymidine phosphorylase (deoA gene) and purine nucleoside phosphorylase (deoD gene) activity, while the deoxyriboaldolase activity controlled by the proximal deoC gene almost does not differ in the rho+ and rho15 strains. The effect of rho15 for the expression of the deo genes in constitutive deoR genome depends on the allele of crp gene: in the crp+ bacteria rho15 leads to a decrease, while in the crp bacteria - to an essential increase in the activity of deo enzymes. These data suggest a possible role of CRP protein as an inhibitor of transcription initiated from deoP promoter. The presence of rho15 in a bacterial genome leads to the complete block of the cytP promoter activity under conditions of both induction of deo enzymes by cytidine and their depression in cytR genome. Based on these data, it is proposed that proximal to cytP promoter, i. e. between deoP and ctyP a Rho-dependent attenuator is located which is usually responsible for termination of the deoP-initiated transcription. An activity of the inner deo operon OP3 promoter is possibly also inhibited in the rho15 genome as shown by the data on the absence of induction of purine nucleoside phosphorylase by inosine in the rho15 bacteria.