Autoregulation of the Escherichia coli replication initiator protein, DnaA, is indirect

Abstract

SummaryThe expression of dnaA is autoregulated, in that transcription of the gene increases when DnaA is inactivated (and initiation of replication prevented) and decreases when DnaA is supplied in excess. However, the inactivation of DnaA does not necessarily lead to increased DnaA production, as dnaA(Ts; temperature sensitive) strains which are integratively suppressed by derivatives of the plasmid R1 do not show temperatureinduced derepression. Several possible explanations for this unanticipated behaviour were considered and ruied out. We suggest here that the completion of a critical step in initiation may prevent dnaA derepression: although DnaA would be required t o complete this step at oriC, DnaA(Ts) would be sufficient at the R1 origin. Autoregulation of dnaA has been attributed to the binding of DnaA at a consensus binding site in the dnaA promoter region. We show here, using reporter systems, that this DnaA-binding site is not required for the autoregulatory response. We find, further, that replacement of the chromosomal dnaA gene with one containing a mutated binding site causes no demonstrable phenotypic change: cells with the mutant gene show no disadvantage in competition with dnaAf cells.

Conditional expression of Mycobacterium smegmatis dnaA, an essential DNA replication gene

“…DnaA is believed to function as a transcriptional regulator of many genes, including itself in E. coli (Messer et al, 1988 ;Messer & Weigel, 1997). The binding of E. coli DnaA to DnaA boxes located in the promoter regions of dnaA and polA has been shown to result in transcriptional repression (Atlung et al, 1984(Atlung et al, , 1985Braun et al, 1985 ;Braun & Wright, 1986 ;Polaczek & Wright, 1990 ;Skovgaard et al, 1998 ;Smith et al, 1997). Scanning the putative promoter regions of several genes, including, for example, dnaA, ftsY and ftsQ of M. smegmatis (Institute of Genome Research ; http :\\www.tigr.org\) and M. tuberculosis (Cole et al, 1998), revealed the presence of several nine nucleotide long sequences with one to two mismatches to the conserved DnaA box sequence TTCA\GGCACA (Madiraju et al, 1999 ;Qin et al, 1999 ;Rajagopalan et al, 1995).…”

Structure and regulation of the dnaA promoter region in three Streptomyces species

“…In vitro as well as in vivo studies revealed that the expression of the dnaA gene is regulated by the interaction of its own protein product with the DnaA boxes (Atlung et al 1985;Braun et al 1985;KuÈ cherer et al 1986). However, a more indirect mode of regulation of the dnaA gene has also been suggested (Herrick et al 1996;Smith et al 1997).…”

DnaA initiator—also a transcription factor

“…Integratively suppressed dnaA ts strains are not derepressed upon heat inactivation of DnaA (Masters et al, 1989). Integratively suppressed dnaA(Null) strains, however, are derepressed (Smith et al, 1997 ). In addition, regulation of dnaA transcription by the DnaA level does not appear to require the integrity of the dnaA-promoter DnaA box because mutation of the box to a sequence that does not bind DnaA does not result in dnaA derepression (Polaczek and Wright, 1990;Smith et al, 1997 ).…”

“…Integratively suppressed dnaA(Null) strains, however, are derepressed (Smith et al, 1997 ). In addition, regulation of dnaA transcription by the DnaA level does not appear to require the integrity of the dnaA-promoter DnaA box because mutation of the box to a sequence that does not bind DnaA does not result in dnaA derepression (Polaczek and Wright, 1990;Smith et al, 1997 ). Possibly other DnaA boxes with a mismatch that are present in the dnaA promoter region may substitute for the box between P1 and P2.…”