The UP element is necessary but not sufficient for growth rate-dependent control of the Escherichia coli guaB promoter

The Escherichia coli guaB promoter (P-guaB) regulates the transcription of two genes, guaB and guaA, that are required for de novo synthesis of GMP, a precursor for the synthesis of guanine nucleoside triphosphates. The activity of P-guaB is subject to growth rate-dependent control (GRDC). Here we show that the A+T-rich sequence located between positions -59 and -38 relative to the guaB transcription start site stimulates transcription from P-guaB similar to 8- to 10-fold and, in common with other UP elements, requires the C-terminal domain of the RNA polymerase alpha subunit for activity. Like the rrnB PI UP element, the P-guaB UP element contains two independently acting subsites located at positions -59 to -47 and -46 to -38 and can stimulate transcription when placed upstream of the lacP1 promoter. We reveal a novel role for the P-guaB UP element by demonstrating that it is required for GRDC. The involvement of the UP element in GRDC also requires the participation of sequences located at least 100 bp upstream of the guaB transcription start site. These sequences are required for down-regulation of P-guaB activity at lower growth rates.