In E. coli Hfr Kavalli (met-) turnover of mRNA was studied in normal state and in methionine deficiency. This strain of E. coli was shown to have the 'loose' type of regulation of RNA synthesis (RC-). Without methionine in E. coli Hfr the rate of the protein synthesis was about 7-8% of that found in the control culture. In studies of the total mRNA turnover the half-life of matrices was equal to 2 min at 37degree, if a medium did not contain methionine; the same value was observed in the control culture. At the same time in methionine starvation an increase in amount of rapidly labelled RNA was observed; the RNA remained stable under simultaneous effect of actinomycin D. This rapidly labelled, stable RNA was the messenger-RNA, associated with cytoplasmic membranes. The hypothesis is advanced that membrane-associated and cytoplasmic RNA are those two types of matrices, which differed in their stability when the protein synthesis was inhibited.