A ribosome-independent stringent factor from bacillus stearothermophilus and a low molecular weight substance inhibitory to its activity

Abstract

In many bacterial strains the level of guanosme 5’-drphosphate, 3’-diphosphate (ppGpp) and the rate of rRNA and tRNA synthesis are apparently correlated suggestmg that the strmgent control system 1s mvolved in the process of regulation of ribosomal gene expression (revrewed [ 1,2]). In relA’ strains ofEscherzkhia coli (p)ppGpp 1s accumulated dunng starvation for the required ammo acrds which in turn leads to restrrction of synthesis of rRNA, tRNA and certam species of mRNA. While relA mutant strains no longer responded to ammo acid starvation, they do restrict rRNA synthesis in response to nutntronal changes during whrch they accumulate (p)ppGpp [3--S]. Apparently the tngger srgnal for (p)ppGpp production varies with strams. It has been shown [6] that m relA’ strams synthesis of (p)ppGpp is catalyzed by the stringent factor whrch transfers pyrophosphate from pppA to (p)ppG, this nbosome-associated factor 1s activated when uncharged tRNA is codon-specrfically bound to the rrbosomes [7-91. A simrlar mechamsm has not yet been found m reZAstrams [6,10] whrch may indicate that the factor from reZAstrain 1s erther highly labrle and mactrvated durmg preparation or that (p)ppGpp 1s synthesized via a different process. Such a drfferent process has been found in Bacillus brevis [ 111 and Streptomyces strazns [ 121 where (p)ppGpp 1s synthesized m a ribosome-mdependent manner. In contrast to the E cnh stnngent factor