Coupling of transcription and replication machineries in λ DNA replication initiation: evidence for direct interaction of Escherichia coli RNA polymerase and the λO protein

Transcription proceeding downstream of the λ phage replicationorigin was previously shown to support initial steps of the λ primosomeassembly in vitro and to regulate frequency and directionality of λ DNA replicationin vivo. In this report, the data are presented indicating that the RNA polymeraseβ subunit makes a direct contact with the λO protein, a replicationinitiator of λ phage. These results suggest that the role of RNA polymeraseduring the initiation of λ phage DNA replicationmay be more complex than solely influencing DNA topology. Results demonstrated in this study also show that gyrase supercoiling activity stimulates the formation of a complex between λO and RNA polymerase, suggesting that the introduction of negative supercoils by DNA gyrase, besides lowering the energy required for DNA strand separation, may play an additional role in modeling protein–protein interactions at early steps of DNA replicationinitiation.