The structure of an integrated copy of the giant linear plasmid SCP1 in the chromosome of Streptomyces coelicolor 2612

In NF strain 2612 of Streptomyces coelicolor, a giant linear plasmid SCP1 is integrated into the chromosome at the 9 o'clock position. To characterize the integrated structure of SCP1, cloning and sequence analysis of the two junctions between the SCP1 DNA and the chromosomal DNA was carried out. The left junction was revealed to retain an almost intact left terminus of SCP1. On the other hand, the right junction was composed of IS 466, deleting completely the right terminal inverted repeat of SCP1. This junction might have been formed by recombination of two IS 466 elements, one present at the end of the right terminal inverted repeat of SCP1 and one on the chromosome. Based on these results, we have proposed a model for the integration of SCP1 into the chromosome. The unique conjugal transfer of NF strains and the origin of the chromosomal antibiotic biosynthetic genes in Streptomyces species are also discussed in relation to this model.