Expression of a DNA strand initiation sequence of ColE1 plasmid in a single-stranded DNA phage

In order to investigate initiation of H-strand (lagging strand) replication of the plasmid ColE1, the origin region fragment (Hae II-E) of ColE1 was inserted into the intergenic region of filamentous DNA phage M13 and cloned. A site capable of promoting DNA strand initiation on a single-stranded DNA template has been detected on the L-strand (leading strand) of the cloned fragment. The site, named rri-1 rifampicin-resistant initiation), directs conversion of chimeric phage single-stranded DNA to parental replicative form in the presence of rifampicin, which blocks the function of the complementary strand origin of M13. The function of rri-1 is dependent on both the dnaG and dnaB gene products. It is postulated that rri-1 might be an initiation site for synthesis of the lagging DNA strand during unidirectional replication of ColE1 DNA.