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 i n the Escherichia coli chromosome. Here, we demonstrate that SeqA stimulate s transcription from the bacteriophage lambda p(R) promoter both in vivo an d in vitro. The activity of the lambda p(L) promoter was found not to be af fected by this protein. SeqA-mediated stimulation of p(R) was dependent on the state of template methylation: transcription was activated on fully met hylated and hemimethylated templates but not on an unmethylated template. U sing electrophoretic mobility shift assay and electron microscopy, we demon strated that SeqA interacts specifically with a p(R) promoter region locate d on both fully methylated and hemimethylated DNA molecules, but not on unm ethylated DNA. The activity of SeqA was found to affect the initiation of l ambda plasmid replication positively in vivo, probably via p(R)-dependent e xpression of lambda replication genes and transcriptional activation of ori lambda. We conclude that, apart from its function in the control of DNA re plication, SeqA is also a specific transcription factor.