Variation in the replication loci of Streptomyces linear plasmids.

Streptomyces linear plasmids start replication at centrally located loci, usually consisting of iterons and adjacent rep genes. Here, we identified four new replication loci from Streptomyces linear plasmids. A discontinuous locus, consisting of two genes and iterons separated by two nonessential genes, was required for replication of pRL2 in both linear and circular modes. A temperature-sensitive plasmid, pRL4, contained a replication locus, a noncoding sequence and a SAP1.35-like gene. A telomere-adjacent locus, another noncoding sequence and SAP1.1-like gene, was identified for replication of the large plasmid pFRL2. The replication locus of pSHK1 consisted of SCP1-rep-like genes and iterons. These results indicate an unexpected variety of components, positions and combinations of replication loci among Streptomyces linear plasmids.