The linear plasmid pPZGlOl of Streptomyces rimosus R6 was restriction mapped with the enzymes Asel, Bfrl, Dral and Xbal. It is 387 kb in size and the ends are inverted repeats of a t least 95 kb in length. Twenty spontaneous morphological variants and seventeen auxotrophic mutants were screened for changes in the plasmid. Two strains were found that had lost all plasmid sequences. Four strains had integrated parts of the plasmid into the chromosome. Restriction analysis suggested that at least three of the integrated strains had retained free plasmid ends. If it is assumed that the chromosome of S. rimosus R6 is linear, this might be explained by replacement of one or both chromosome ends by a plasmid end. One strain, which overproduced oxytetracycline, carried an enlarged linear plasmid of 1 Mb in size that had acquired chromosomal sequences from the oxytetracycline biosynthesis cluster.

A restriction map of the 8 Mb linear chromosome of Streptomyces rimosus R6-501 was constructed for the enzymes Asel (13 fragments) and DraI (7 fragments). Linking clones for all 12 Asel sites and 5 of the 6 DraI sites were isolated. The chromosome has terminal inverted repeats of 550 kb, which are the longest yet reported for a Streptomyces species. The oxytetracycline gene cluster lies about 600 kb from one end, which might account for its frequent spontaneous amplification and deletion. Several other markers were localized on the chromosome (dnaA and red, the mn operons, the attachment site for pSAM2 and prophages RP2 and RP3). Comparison of the conserved markers with the map of Streptomyces coelicolor A3(2) suggested there are differences in genome organization between the two species.