TRANSCRIPTION REGULATION BY INITIATING NTP CONCENTRATION - RIBOSOMAL-RNA SYNTHESIS IN BACTERIA

The sequence of a promoter determines not only the efficiency with whi ch it forms a complex with RNA polymerase, but also the concentration of nucleoside triphosphate (NTP) required for initiating transcription . Escherichia coli ribosomal RNA (rrn PI) promoters required high init iating NTP concentrations for efficient transcription because they for m unusually short-lived complexes with RNA polymerase; high initiating NTP concentrations [adenosine or guanosine triphosphate (ATP or GTP), depending on the rrn P1 promoter] are needed lo bind to and stabilize the open complex. ATP and GTP concentrations, and therefore rrn P1 pr omoter activity, increase with growth rate. Because ribosomal RNA tran scription determines the rate of ribosome synthesis, the control of ri bosomal RNA transcription by NTP concentration provides a molecular ex planation for the growth rate-dependent control and homeostatic regula tion of ribosome synthesis.