Identification of essential genes for linear replication of an SCP1 composite plasmid

The 365 023 bp linear plasmid Streptomyces coelicolor plasmid 1 (SCP1) of S. coelicolor A3(2) belongs to the model systems of actinomycetes linear plasmids. Although the plasmid was detected more than two decades ago, little functional information about replication and maintenance of the linear topology exists. Here, for the first time, is the description of a region in SCP1 that is essential for linear replication of the plasmid. The SCP1 linear replication (Slr) region contains three putative genes. Intriguingly, one of the genes, SlrC, does show homology to PPA1294 of Propionibacterium acne that possesses a conserved DNA_pol_B_2 domain, which is found in organellar and viral DNA polymerases as, for example, in the Bacillus phi29 polymerase.