A linear plasmid-like DNA was isolated by Agarose gel electrophoresis from a lysate of Streptomyces sp. 7434-AN4 which produces lankacidin group antibiotics. The DNA (pSLA2) with a molecular weight of 11.2 x 106 was cleaved into five and three fragments, respectively, with XmaI and BamNI on the definite sites from the end, but not digested by EcoRI and HindIII. Upon treatment of the strain with ethidium bromide, variants were obtained which have lost the ability to produce the antibiotics. These variants were found to have lost pSLA2. These results suggest that the linear plasmid-like DNA is involved in the production of lankacidin group antibiotics.Since the first observation by OKANISHI et al.(1) that plasmids may be involved in the production of kasugamycin and aureothricin, lines of evidence have accumulated on plasmid involvement in antibiotic production (2, 3). These observations are based on genetic analysis (4, 5) or on the loss of antibiotic production by host cells upon treatment with curing agents (1, 6). In several antibiotic-producing Streptomyces species (3, 7, 8), extrachromosomal DNA elements have been found as covalently closed circular (ccc) DNA.We have extended these studies by screening 34 antibiotic-producing strains of Streptomyces for plasmid, in order to obtain further insight into possible involvement of plasmids in antibiotic production. During these processes, we found a linear plasmid-like DNA which may be involved in the production of lankacidin group antibiotics. Results obtained are described in this paper.

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