SeqA, the Escherichia coli origin sequestration protein, is also a specific transcription factor

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Abstract
The SeqA protein is a negative regulator of initiation of DNA replication in the Escherichia coli chromosome. Here, we demonstrate that SeqA stimulates transcription from the bacteriophage λpR promoter both in vivo and in vitro. The activity of the λpL promoter was found not to be affected by this protein. SeqA-mediated stimulation of pR was dependent on the state of template methylation: transcription was activated on fully methylated and hemimethylated templates but not on an unmethylated template. Using electrophoretic mobility shift assay and electron microscopy, we demonstrated that SeqA interacts specifically with a pR promoter region located on both fully methylated and hemimethylated DNA molecules, but not on unmethylated DNA. The activity of SeqA was found to affect the initiation of λ plasmid replication positively in vivo, probably via pR-dependent expression of λ replication genes and transcriptional activation of ori λ. We conclude that, apart from its function in the control of DNA replication, SeqA is also a specific transcription factor.