rpoB mutation in Escherichia coli alters control of ribosome synthesis by guanosine tetraphosphate

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Abstract
An isogenic pair of relA+ and relA strains of E. coli B/r with a mutation in the RNA polymerase subunit gene rpoB (Rif) was isolated in which the relationship between guanosine tetraphosphate (ppGpp) concentration and stable RNA (rRNA, tRNA) gene activity was altered. The RNA polymerase in the ropB strains is .apprx. 20-fold more sensitive to ppGpp with respect to its stable RNA promoter activity than was the wild-type enzyme. The existence of such mutants is consistent with the idea that ppGpp interacts with the RNA polymerase enzyme and alters its promoter selectivity, i.e., reduces its affinity for the stable RNA promoters. Under most conditions, the rpoB mutants had a reduced rate of growth and about a 10-fold-reduced intracellular concentration of ppGpp compared with the ropB wild-type strains. The reduction of the level of ppGpp in the ropB mutants during exponential growth was presumably a reflection of an indirect effect of the rpoB mutation on the control of relA-independent ppGpp metabolism.