DnaA and SeqA proteins are main regulators (positive and negative, respectively) of the chromosome replication in Escherichia coli. Nevertheless, both these replication regulators were found recently to be also transcription factors. Interestingly, both DnaA and SeqA control activity of the bacteriophage lambdap(R) promoter by binding downstream of the transcription start site, which is unusual among prokaryotic systems. Here we asked what are functional relationships between these two transcription regulators at one promoter region. Both in vivo and in vitro studies revealed that DnaA and SeqA can activate the p(R) promoter independently and separately rather than in co-operation, however, increased concentrations of one of these proteins negatively influenced the transcription stimulation mediated by the second regulator. This may suggest a competition between DnaA and SeqA for binding to the p(R) regulatory region. The physiological significance of this DnaA and SeqA-mediated regulation of p(R) is demonstrated by studies on lambda plasmid DNA replication in vivo.
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