The effect of DnaA protein levels and the rate of initiation at oriC on transcription originating in the ftsQ and ftsA genes: in vivo experiments.

The DnaA protein of Escherichia coli, essential for initiation at oriC, binds at a defined sequence which occurs at the chromosomal origin, near plasmid replication origins and in the promoters of the dnaA and mioC genes. This sequence also occurs at many other sites on the E. coli chromosome including three sites within the essential cell division genes ftsQ and A. Using an fts-lac fusion phage, lambda JFL100, we show here that fts gene expression responds both to reduced and increased intracellular levels of DnaA protein in a manner consistent with the hypothesis that DnaA protein regulates fts gene expression. Experiments using dnaC and dnaB-ts strains, however, suggest that DnaA control of fts transcription may be indirect, at least in part, with fts responding to the rate of initiation at oriC as well as to changes in DnaA protein level per se. It differs in this respect from dnaA gene expression which is unaffected when initiation of replication is inhibited by DnaB or DnaC inactivation. Strains integratively suppressed with pKN500 behave anomalously; neither fts nor dnaA transcription is significantly increased when DnaA is inactivated in these strains.