Cell cycle-dependent transcription from the gid and mioC promoters of Escherichia coli.

Transcription from the gid and mioC promoters, which neighbor the origin of replication of the Escherichia coli chromosome (oriC), has been implicated in the control of initiation of replication of minichromosomes. The amounts of transcripts from these two promoters on the chromosome were quantified at various times in a synchronized culture of a temperature-sensitive dnaC mutant strain. Transcription from the gid promoter was most active before the initiation of replication and was inhibited after initiation, during the time corresponding to the period of sequestration of the oriC region from the dam methyltransferase. On the other hand, transcription from the mioC promoter was inhibited before initiation and the inhibition was relieved after initiation prior to the recovery of gid transcription. The strict regulation of transcription from the gid and mioC promoters may be involved in positive and negative control of chromosomal replication, respectively, as has been suggested for minichromosome replication. The DnaA protein was involved in repression of mioC transcription, indicating that the activity of the DnaA protein changes during the cell cycle.