The mechanism of action of ppGpp on rRNA synthesis in vitro

The mediator for stringent control, ppGpp, binds to the β‐subunit of Escherichia coli RNA polymerase

“…Biochemical and genetic studies carried out thus far have not provided evidence for a classical repressor protein or sigma factor(s) to mediate the stringent response. Instead, the results of several experiments have suggested that the site of action of ppGpp is RNA polymerase during various stages of transcription (Cashel 1970;van Ooyen et al 1976;Hamming et al 1980;Pao et al 1980;Kingston & Chamberlin 1981;Lamond & Travers 1985;Bremer et al 1987); however, a direct demonstration of their interaction is still lacking. Interestingly, it was observed that E. coli mutants which have been deleted for relA and spoT, leading to an abolition of ppGpp synthesis, are unable to grow in minimal media in the absence of multiple amino acid supplements (Xiao et al 1991).…”

Increased Mutation Frequency in Redox-Impaired Escherichia coli Due to RelA- and RpoS-Mediated Repression of DNA Repair

“…Specifically, proline transport genes (proW) and proline tRNA (proL) showed the greatest positive (log 2 ratio ϭ 6.42) and negative (log 2 ratio ϭ Ϫ5.45) changes in expression in the mutant relative to the level for the wild-type parent. One crucial difference is that contrary to the inhibition of the ribosome synthesis during the stringent response (10,15,17,37,67,68,70), we observed increases in the expression levels of genes involved in translation and ribosomal structure (Fig. 2).…”

“…The stringent response in E. coli in response to amino acid starvation is characterized by a rapid inhibition of rRNA and tRNA synthesis and upregulation of the metabolic genes (15,17,37,68). The stringent-response messenger (p)ppGpp, synthesized by the association of the stringent factor relA with the ribosomal protein L11, binds to the ␤ subunit of RNA polymerase to modulate the expression of over a third of all E. coli genes (10,67,68,70). The interdependence of the RpoS-mediated stress response and the stringent response is well documented (35).…”

ppApp alters transcriptional selectivity of Escherichia coli RNA polymerase

“…In vitro the functional interaction of ppGpp with RNA polymerase is apparently at least biphasic, for whereas the k'i for the selective inhibition of rRNA synthesis is -1O-4 M [6,7] that for the inhibition of sutI tRNA transcription [8] and of poly d(I-C) directed GpCpC formation [ 161 is -5 X 10m6 M. Figure 1 shows that, in agreement with [6,7], addition of 2 X 10V4 M ppGpp greatly increased the inhibition of rRNA transcription by increasing salt concentration.…”