Pock-forming plasmids isolated from streptomyces roseochromogenus.

A series of high copy number plasmids designated pSRC were isolated from Streptomyces roseochromogenus S264. The pSRC series were found to be self-transmissible by conjugation and to elicit lethal zygosis (Ltz). Using the Ltz phenotype to detect plasmid transformants, the pSRC plasmids were shown to have a wide host range. Among them pSRC1 consisted of two different plasmids with the same molecular weight, pSRC1a and 1b. Information regarding restriction sites suitable for the insertion of DNA was obtained by cloning the thiostrepton resistance gene from pIJ702 into pSRC1b. The single Bgl II site of pSRC1b was nonessential for replication and pock-formation. The pSRC plasmids may be suitable as cloning vectors in Streptomyces.