GROWTH RATE-DEPENDENT CONTROL OF THE RRNB P1 CORE PROMOTER IN ESCHERICHIA-COLI

We have extended our previous studies of the DNA sequences required fo r growth rate-dependent control of rRNA transcription in Escherichia c oli. Utilizing a reporter system suitable for evaluation of promoters with low activities, we have found that the core promoter region of rr nB P1 (-41 to +1 with respect to the transcription initiation site) is sufficient for growth rate-dependent control of transcription, both i n the presence and in the absence of guanosine 3'-diphosphate 5'-dipho sphate (ppGpp). The core promoter contains the -10 and -35 hexamers fo r recognition by the sigma 70 subunit of RNA polymerase but lacks the upstream (UP) element, which increases transcription by interacting wi th the alpha subunit of RNA polymerase. It also lacks the binding site s for the positive transcription factor FIS. Thus, the UP element, FIS , and ppGpp are not needed for growth rate-dependent regulation of rRN A transcription. In addition, we find that several core promoter mutat ions, including -10 and -35 hexamer substitutions, severely reduce rrn B P1 activity without affecting growth rate-dependent control. Thus, a high activity is not a determinant of growth rate regulation of rRNA transcription.