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

Abstract

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.

Transcription of the ftsZ gene and cell division in Escherichia coli

“…The ftsZ::lacZ operon fusion we used in our experiments was constructed by J. Lutkenhaus; it is carried on the phage XJFL100, which has been described previously (5,24). In this construction (see Fig.…”

“…4) (14). Furthermore, when replication initiation is blocked, ftsZ expression is stimulated (24). The nature of the putative regulatory event leading to the doubling in the rate offtsZ transcription is under study.…”

“…Furthermore, Donachie et al (5) have reported that ftsZ transcription is indeed stimulated during the expression of mutations in certain genes in the 2-min cluster, including ftsI (pbpB), ftsA, ftsQ, and ftsZ itself. Other transcriptional regulation has also been reported for the ftsZ gene, by the cyclic AMP-catabolite gene activator protein complex (5) and by the DnaA protein (24). In the present work, we have reexamined the regulation by products of fts genes with the intention of trying to determine whether the reported regulation results from the absence of * Corresponding author.…”

“…They are described in Table 1. Strain AB1157 was lysogenized with phage XJFL100, which carries anftsZ: :lacZ operon fusion (24) curing. We chose one such lysogen and selected a tonA derivative by resistance to phage T5; this strain was named GC3439.…”

DnaA initiator—also a transcription factor

“…DnaA binds to this box, as demonstrated by DNase I footprinting and by gel retardation analyses. Inactivation of DnaA protein in temperature-sensitive dnaA (dnaA ts ) strains results in derepression of the dnaA promoters, whereas overproduction of DnaA from a plasmid represses dnaA transcription (Braun et al, 1985;Atlung et al, 1985;Kü cherer et al, 1986;Masters et al, 1989). Increasing the number of intracellular DnaA-binding sites by introduction of a high-copynumber plasmid containing DnaA boxes also results in dnaA derepression, apparently by titration of DnaA (Hansen et al, 1987 ).…”