Growth phase and growth rate dependence of ribosomal peptidyltransferase activity status in Escherichia coli

Abstract

Ribosomes from a clinical isolate of E coli were purified and characterized. The structural features of these ribosomes were identical to wild-type E coli ribosomes, with the exception that rRNA in general, but especially 23S rRNA, was degraded as a result of the transition from early to late logarithmic growth phase, on different growth media. Analysis of the ribosomal protein by gel electrophoresis indicated that the L12/L7 molar ratio increases during early logarithmic phase, reaching a maximum value of about 1.6 at midlogarithmic phase, and then falling to 0.7 in late logarithmic phase. Concomitantly with L12/L7 alterations, the activity status of ribosomal peptidyltransferase was found to undergo a striking shift. Reconstitution experiments demonstrated that the two effects are closely related. Moreover, L12/L7 molar ratio as well as peptidyltransferase activity increased with increasing growth rate. In the latter case, however, the acetylation level of L12 protein per se seemed to be inadequate to modulate the peptidyltransferase activity.