DnaA-stimulated transcriptional activation of oriλ:: Escherichia coli RNA polymerase β subunit as a transcriptional activator contact site

We present evidence that Escherichia coli RNA polymerase beta subunit may be a transcriptional activator contact site. Stimulation of the activity of the p(R) promoter by DnaA protein is necessary for replication of plasmids derived from bacteriophage lambda. We found that DnaA activates the p(R) promoter in vitro. Particular mutations in the rpoB gene were able to suppress negative effects that certain dnaA mutations had on the replication of lambda plasmids; this suppression was allele-specific. When a potential DnaA-binding sequence located several base pairs downstream of the p(R) promoter was scrambled by in vitro mutagenesis, the p(R) promoter was no longer activated by DnaA both in vivo and in vitro. Therefore, we conclude that DnaA may contact the beta subunit of RNA polymerase during activation of the p(R) promoter. A new classification of prokaryotic transcriptional activators is proposed.