Polyribosomes and control of protein synthesis: Effects of sodium fluoride and temperature in reticulocytes

Abstract

Reticulocytes from phenylhydrazine-treated rabbits were pre-incubated with 0·01 M -sodium fluoride to inhibit protein synthesis and dissociate polyribosomes to 80 s ribosomes. Upon incubation of these cells without fluoride, protein synthesis is restored and reaches rates comparable to control cells (not pre-incubated with fluoride) within three minutes at 37°C when only a fraction of the polyribosomes have re-formed. In these cells, polyribosome content and polyribosome size may continue to increase for 60 to 120 minutes at 37°C without a change in rate of protein synthesis. As polyribosome content increases, the specific activity of the polyribosomes remains constant. These data indicate that in these cells polyribosome content is not the factor which limits the rate of protein synthesis. An estimate of the time for globin chain synthesis indicates that it increases progressively as polyribosome content increases. The protein synthesized during polyribosome formation in fluoride pre-incubated cells is predominantly globin and, by sedimentation and chromatographic characteristics, indistinguishable from the protein synthesized in control cells. The effect of the temperature of incubation on protein synthesis by reticulocytes was examined. In contrast to the alterations in polyribosomes with a constant rate of protein synthesis during recovery from the “fluoride effect”, increasing the temperature of incubation of reticulocytes between 17 and 37°C is associated with no change in polyribosome size or content, but an increase in polyribosome specific activity and in rate of protein synthesis. The data are interpreted in terms of mechanisms which might alter polyribosome size, content and/or function in reticulocytes which synthesize no RNA.