Effects of Guanosine Tetraphosphate, Guanosine Pentaphosphate, and β -γ Methylenyl-Guanosine Pentaphosphate on Gene Expression of Escherichia coli in vitro
Abstract
The effects of guanosine tetraphosphate (ppGpp) and guanosine pentaphosphate (pppGpp), both produced by E. coli, were measured on the activities of several genes in a cell-free system. Gene activity is measured as gene-directed synthesis of biochemically competent protein or transfer RNA. Both ppGpp and pppGpp stimulated the activities of the ara, lac, and trp operons and inhibited the arg operon. Production of transfer-RNATyr was unaffected by moderate levels of either ppGpp or pppGpp and only slightly inhibited at higher levels of ppGpp. Since the cell-free reaction mixtures hydrolyze pppGpp to ppGpp, we performed similar studies with a hydrolysis-resistant analog of pppGpp, the β-γ methylenyl derivative (pcppGpp). In general, pcppGpp shows the same inhibitory potency as pppGpp for the arg operon, but lacks the stimulatory effects on the ara, lac, and trp operons. This result suggests that the stimulation of these gene activities is specific for ppGpp. Under similar conditions, pppGpp and ppGpp show a slight inhibitory effect on the messenger-directed synthesis of β-galactosidase and no effect on the messenger-directed synthesis of MS2 viral-coat protein. These observations, together with the fact that in the same system these nucleotides affect coupled transcription and translation, lead us to surmise that the activities of pppGpp and ppGpp are exerted at the level of RNA polymerase activity.
- Publication:
-
Proceedings of the National Academy of Science
- Pub Date:
- January 1974
- DOI:
- 10.1073/pnas.71.1.63
- Bibcode:
- 1974PNAS...71...63Y