[Stringent RNA polymerase of E. coli and its in vivo transcriptional activity].

Several spontaneous E. coli mutants with the similar phenotype as that in the condition of amino acid deficiency were obtained on the selective media. One of the mutants (LCH001) showing slow growth phenotype on LB agar plate and pink or white colonies on MacConkey agar plate was mapped at rpoC gene encoding the beta' subunit of RNA polymerase by phage P1 transduction and transformation assays and found to be a new site mutation from G to T at 3406bp in the rpoC gene, which resulted in the amino acid change from Glycine (GGT) to Cysteine (TGT). The effect of the mutation on transcriptional activity of both stringent and non-stringent controlled promoters in vivo was measured by determining the beta-galactolactase activity of the growing cells. Results showed that the transcriptional activity of the mutant LCH001 reduced greatly on the stringent promoter, but increased significantly on the non-stringent promoter. The beta-galactolactase activity of the mutant LCH001 transcribed on stringent promoter was 18% lower, but 5-fold higher on the non-stringent controlled promoter than that of the wild-type strain CLT5034. This finding may give insights into future studies of the structure-function relationship of RNA polymerase as well as its role in the stringent response of bacteria.