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Autoregulation of the Escherichia coli replication initiator protein, DnaA, is indirect
Author(s) -
Smith R. W. P.,
McAteer Sean,
Masters Millicent
Publication year - 1997
Publication title -
molecular microbiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.857
H-Index - 247
eISSN - 1365-2958
pISSN - 0950-382X
DOI - 10.1046/j.1365-2958.1997.3121675.x
Subject(s) - dnaa , derepression , biology , plasmid , dna binding protein , gene , mutant , dna replication , microbiology and biotechnology , origin of replication , genetics , gene expression , transcription factor , psychological repression
Summary The 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(7s; temperature sensitive) strains which are integratively suppressed by derivatives of the plasmid R1 do not show temperature‐induced derepression. Several possible explanations for this unanticipated behaviour were considered and ruled out. We suggest here that the completion of a critical step in initiation may prevent dnaA derepression: although DnaA would be required to 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 autoregu‐latory response. We find, further, that replacement of the chromosomal dnaA gene with one containing a mutated binding site causes no demonstrable pheno‐typic change: cells with the mutant gene show no disadvantage in competition with dnaA + cells.