Increased stability of polysomes in an Escherichia coli mutant with relaxed control of RNA synthesis.

When cells of Escherichia coli auxotrophs are starved for a required amino acid, the net synthesis of RNA ordinarily ceases at once.However, a fortuitously en- countered mutant continues to accumulate RNA, at a substantial fraction of the normal rate, when starved for methioninel or for various other amino acids,2 and this mutant has been designated2 as "relaxed" in the control of RNA synthesis (RCrel).The mechanism responsible for this control, and for its alteration in the relaxed mutant, has not yet been satisfactorily established.This problem, and our recent observation of a stimulatory effect of methionine on RNA synthesis in certain strains,3 has led us to explore the possibility that the level of free ribosomes (i.e., those not engaged in polysomes) might control by direct feedback the syn- thesis of ribosomal RNA (rRNA).This approach was encouraged by the recent report of Weber and DeMoss,4 which we have confirmed, that starvation of an E. coli auxotroph for a required amino acid results in a substantial shift of ribosomes from polysomes to the monosome peak.The present paper shows that in an RCrel strain, in contrast, a high polysome level is maintained during starvation for an amino acid.Following the completion of this work, we learned (personal com- munication) that similar observations have recently been made by Morris and DeMoss.5