STRINGENT CONTROL AND GROWTH-RATE-DEPENDENT CONTROL HAVE NONIDENTICALPROMOTER SEQUENCE REQUIREMENTS

Escherichia coil uses at least two regulatory systems, stringent contr ol and growth-rate-dependent control, to adjust rRNA output to amino a cid availability and the steady-state growth rate, respectively, We ex amined transcription from rrnB P1 promoters containing or lacking the cis-acting UP element and FIS protein binding sites after amino acid s tarvation, The ''core promoter'' responds to amino acid starvation lik e the full-length wild-type promoter; thus, neither the UP element nor FIS plays a role in stringent control, To clarify the relationship be tween growth-rate-dependent regulation and stringent control, we measu red transcription from growth-rate-independent promoters during amino acid starvation, Four rrnB P1 mutants defective for growth-rate contro l and two other growth-rate-independent promoters (rrnB P2 and pS10) s till displayed stringent regulation. Thus, the two systems have differ ent promoter determinants, consistent with the idea that they function by different mechanisms, Two mutations disrupted stringent control of rrnB P1: (i) a multiple base change in the ''discriminator'' region b etween the -10 hexamer and the transcription start site and (ii) a dou ble substitution making the promoter resemble the E sigma(70) consensu s promoter. These results have important implications for the mechanis ms of both stringent control and growth-rate-dependent control of rRNA transcription.