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

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 lambda p(R) promoter both in vivo and in vitro. The activity of the lambda p(L) promoter was found not to be affected by this protein. SeqA-mediated stimulation of p(R) 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 p(R) 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 lambda plasmid replication positively in vivo, probably via p(R)-dependent expression of lambda replication genes and transcriptional activation of ori lambda. We conclude that, apart from its function in the control of DNA replication, SeqA is also a specific transcription factor.