SEPARATION BY PULSED-FIELD GRADIENT GEL ELECTROPHORESIS OF GIANT LINEAR PLASMIDS FROM ANTIBIOTIC-PRODUCING STRAINS OF STREPTOMYCES AND NOCARDIA

Eleven strains belonging to either Streptomyces or Nocardia were examined for the presence of giant linear plasmid(s) by pulsed-field gel electrophoresis with a 'home-made' apparatus. Such a plasmid could be detected only in S. coelicolor (where its presence is already known) and in S. rimosus. The size of the S. rimosus plasmid was estimated to be 255 kb, which makes it somewhat smaller than the S. coelicolor 320 kb plasmid. Nick-translated S. rimosus plasmid DNA hybridizes mainly with the plasmid and faintly with the chromosomal DNA. It does not hybridize with either the chromosomal or plasmid DNA of S. coelicolor, suggesting that the latter is an altogether different plasmid. Since S. rimosus is an antibiotic-producing strain, there is a possibility, if not the likelihood, that the genes for antibiotic production may be located on the giant plasmid detected.