Abstract
During glucose-lactose diauxie lag, Escherichia coli synthesizes ribonucleic acid (RNA) at about 7% of the rate in exponentially growing cells. RNA synthesis could be restored to the log-phase rate within 3 min after the addition of glucose to the culture (shift-up). This stimulation occurred equally well in the presence of chloramphenicol and therefore did not require the synthesis of new proteins. RNA synthesis could also be stimulated by the addition of glycerol, but only after a delay of 15 to 20 min. Glycerol stimulation occurred more rapidly in cells preadapted by prior growth on glycerol and occurred immediately in a mutant (glpR) constitutive for the enzymes of glycerol catabolism. Measurement of a parameter related to the rate of initiation of stable (ribosomal and transfer) RNA chains showed that the initiation of transcription of these stable RNA species was completely inhibited during the diauxie lag, but could be restored to the rate characteristic of log-phase cells by shift-up with glucose. Sucrose gradient analysis of RNA purified from cells after a glucose shift-up indicated an increased rate of accumulation of the ribosomal and transfer RNA species. It is proposed that a specific mechanism to inhibit the initiation of transcription of ribosomal and transfer RNA operates during diauxie lag. This inhibitory mechanism is governed by the level of cellular energy resources insofar as the inhibition is readily reversed by metabolizable energy sources.