Transient rates of synthesis of individual polypeptides in E. coli following temperature shifts

Abstract

The effect of temperature shifts on the rates of synthesis of selected individual polypeptides in wild-type E. coli was studied through pulse-labeling and resolution of protein by the O'Farrell two-dimensional gel system.The overall rate of protein synthesis quickly accelerated to its new steady state rate after temperature shifts, but the differential rates of synthesis of most individual polypeptides studied either increased transiently (as much as 50 fold) or decreased transiently (as much as 10 fold). Their new steady state values, usually the pre-shift values, were reched 20 min after the shift. The magnitude of the responses depended upon the size of the temperature shift, and a shift downward generated responses opposite to those of a shift upward. The ten aminoacyl-tRNA synthetases and five transcriptional or other translational factors studied responded with greater similarity than did a group of nine unidentified polypeptides chosen from different regulatory classes. Guanosine tetraphosphate accumulated transiently upon a temperature shift upward, but reducing this accumulation did not in general alter the quantitative responses of the polypeptides.For some proteins, these transients accomplish rapid attainment of a new steady state level. Many of the transients seem to be active regulatory responses.