Synthesis of Guanosine Polyphosphates (pppGpp and ppGpp) and Its Regulation by Aminoacyl-tRNA1

Publisher Website
Google Scholar
Abstract
The experiments reported here show a high degree of similarity between the in vitro and in vivo systems of (p)ppGpp synthesis using the supernatant fraction of bacterial homogenate after centrifugation at 30,000 × g (S-30); this fraction contains high levels of aminoacyl-tRNA synthetases. Several in vivo effects on the synthesis of (p)ppGpp can be observed in this system with poly(A) and lysine. In particular, the effect of increasing concentrations of amino acid on the formation of (p)ppGpp was studied in vitro. It was found to be quite similar to the effect in the in vivo system; thus, up to ca. 30% saturation of tRNALys, the formation of (p)ppGpp remains nearly unaffected, then marked inhibition begins, until at ca. 80% saturation (p)ppGpp synthesis falls to ca. 8% of the initial level and becomes nearly stationary when about 85% of the tRNALys present is aminoacylated. This corresponds closely to reports that, in vivo, the tRNA is 30% charged in the absence of the corresponding amino acid and in its presence appears to be not more than 75% charged at most. Furthermore, the S-30 system was used to test the stability of (p)ppGpp using Ercherichia coli (E. Coli) strains which were recently reported to show relatively slow degradation of ppGpp and absence of pppGpp. We found, however, that in the in vitro system, pppGpp is readily formed initially in these strains and is then lost slowly; ppGpp added to the S-30 system did not show degradation. Using S-30 of a stringent E. Coli strain with barely inhibitory concentrations of chloramphenicol, the abnormal loss of (p)ppGpp formation in the presence of very low concentrations of amino acid was observed. It had been found earlier that chioramphenicol in the presence of small amounts of amino acid induces the disappearance of stringent response in vivo.

This publication has 0 references indexed in Scilit: