ISOLATION AND CHARACTERIZATION OF A POCK-FORMING PLASMID pTA4001 FROM STREPTOMYCES LAVENDULAE

A covalently closed circular (ccc) DNA with a size of 5.9 kb was isolated from a strain producing streptothricins, Streptomyces lavendulae No. 1080, and its restriction map was determined. Colonies of the plasmid-carrying strain formed pocks on the lawn of the plasmid-free derivatives of the same organism. The pock-forming ability of pTA4001 was confirmed by transformation of S. lividans with the plasmid DNA. Insertion of the chromosomal streptothricin resistance gene of S. lavendulae No. 1080 into pTA4001 gave various composite plasmids with marked deletion in S. lividans as a host. By analyzing these derivatives, a 2.2 kb region essential for replication and a possible region for pock formation were determined in the map of pTA4001. A cloning vector, pKST2 (4.3 kb) containing resistance genes to streptothricin and thiostrepton with several unique cloning sites was constructed from pTA4001.