A Consequence of the rel Gene during a Glucose to Lactate Downshift in Escherichia coli

Escherichia coli strains with relaxed (CP79) and stringent (CP78) RNA control were examined in regard to their RNA synthesis and accumulation during balanced growth in two media supporting different growth rates, and during downshift transitions between them. Although the RNA content was greater for CP79 at both growth rates, the total rate of RNA synthesis was found to be proportional to the growth rate in both strains. Both strains traversed a downshift transition in about equal periods of time, but as a consequence of the relaxed mutation the reduction of the rate of RNA synthesis in CP79 was much less; the total rate of RNA synthesis was reduced during the downshift to 5% of the preshift rate in CP78 but to only 50% of the preshift rate in CP79. Therefore, cessation of RNA accumulation during the downshift in CP79 implies that considerable RNA degradation was required. Thus, in addition to its function during amino acid starvation, the rel gene increases the efficiency of the transition from fast to slow growth rates.