SeqA limits DnaA activity in replication from oriC in Escherichia coli.
A mutant Escherichia coli that transforms minichromosomes with high efficiency in the absence of Dam methylation has been isolated and the mutation mapped to 16.25 min on the E. coli map. The mutant strain containing seqA2 is defective for growth in rich medium but not in minimal medium. A similar mutation in this gene, named seqA1, has also been isolated. Here we show that the product of the seqA gene, SeqA, normally acts as an inhibitor of chromosomal initiation. In the seqA2-containing mutant, the frequency of initiation increases by a factor of three. Introduction of the wild-type seqA gene on a low-copy plasmid suppresses the cold sensitivity of a dnaAcos mutant known to overinitiate at temperatures below 39 degrees C. In addition, the seqA2 mutation is a suppressor of several dnaA (Ts) alleles. The seqA2 mutant overinitiates replication from oriC and displays the asynchronous initiation phenotype. Also the seqA2 mutant has an elevated level of DnaA protein (twofold). The introduction of minichromosomes or a low-copy-number plasmid carrying five DnaA-boxes from the oriC region increases the growth rate of the seqA2 mutant in rich medium to the wild-type level, reduces overinitiation but does not restore synchrony. We propose that the role of SeqA is to limit the activity level of the E. coli regulator of chromosome initiation, DnaA.
von Freiesleben
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U
Department of Molecular Biology and Microbiology, Tufts University Medical School, Boston, Massachusetts 02111.
Rasmussen
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KV
Schaechter
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M
D001425:Bacterial Outer Membrane Proteins; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D002874:Chromosome Mapping; D004261:DNA Replication / Q000235:genetics; D004269:DNA, Bacterial / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D004926:Escherichia coli / Q000235:genetics / Q000378:metabolism*; D029968:Escherichia coli Proteins; D005434:Flow Cytometry; D005798:Genes, Bacterial; D009154:Mutation; D010641:Phenotype; D010957:Plasmids / Q000235:genetics; D018741:Replication Origin; D014157:Transcription Factors
D001425:Bacterial Outer Membrane Proteins; D001426:Bacterial Proteins; D004269:DNA, Bacterial; D004268:DNA-Binding Proteins; C066312:DnaA protein, Bacteria; D029968:Escherichia coli Proteins; C089746:SeqA protein, E coli; D014157:Transcription Factors