Characterization of the antibiotic resistance plasmid ERL1 from Streptococcus pyogenes

The streptococcal plasmid ERL1 determining inducible resistance to erythromycin, lincomycin, and staphylomycin S was isolated by dye-buoyant density centrifugation and shown to have a molecular weight of about 17.5 Mdal, as revealed by sedimentation through neutral sucrose gradients. In SM60 cells entering the stationary phase its covalently closed circular form was present to the extent of 5 copies per chromosomal genome equivalent. ERL1 was subject to the DNA restriction and modification mechanism discovered in strain 56188. It did not apear to exercise restriction of phage DNA but mediated a partial release of the restricted growth of A25.