Control of ColE1 plasmid replication: enhancement of binding of RNA I to the primer transcript by the Rom protein.

RNA I prevents a transcript (RNA II) from the ColE1 primer promoter to form a hybrid with the template DNA and thereby inhibits formation of primer for DNA replication. Binding of RNA I to RNA II is responsible for the inhibition. The Rom protein, a plasmid-specified 63 amino acid protein, enhances the inhibitory effect of RNA I on primer formation by enhancing the binding of RNA I to RNA II. In vivo, RNA I controls plasmid copy number and incompatibility and inhibits expression of a galK gene fused to the primer promoter. The rom gene modulates these activities of RNA I. These functions of the rom gene can be explained by alteration of the binding of RNA I to RNA II by the Rom protein.