Metabolic Stability of the Two Forms of Initiation Factor IF‐3 in Escherichia coli during the Growth Cycle

Abstract

Possible alteration in the ratio of the long and short forms of initiation factor IF-3 during the growth cycle of E. coli was examined. The ratio remained unchanged between the exponential and stationary growth phases. Contrary to an earlier report, the total amount of IF-3 relative to the ribosome content in stationary phase cells was essentially the same as in midlog phase cells. The activity of IF-3, assayed after its separation from other initiation factors by chromatography, was also the same in extracts from midlog and stationary phase cells. In E. coli the ratio of IF-3/ribosome is apparently maintained constantly. The ribosomes themselves retained virtually full activity in vitro during this transition indicating that growth-cycle-dependent biochemical modifications of the ribosome do not affect its protein synthetic capacity per se.