Relationship between the replication functions of Streptomyces plasmids pJV1 and pIJ101.

The essential replication region of the Streptomyces phaeochromogenes plasmid pJV1 was sequenced and compared to the equivalent region of the well-characterized Streptomyces plasmid pIJ101. The sequence revealed a similar organization in both plasmids, including a conserved region within both plasmid origins, which is just upstream of a gene encoding the replication protein (Rep). The Rep proteins of pJV1 and pIJ101 are very similar, and both have a conserved motif, also present in Rep proteins of single-stranded DNA plasmids of the low G + C gram+ bacteria that includes a tyrosine residue presumably involved in creating the single-stranded nick that initiates the replication event. A co-integration experiment between these two replicons led to the formation of a novel replicon with a hybrid origin and allowed the identification of the nick site where replication starts, also showing that the replication functions of both plasmids are related.