Nucleotide sequence of conjugative and integrating plasmid pSLS from streptomyces laurentii ATCC31255

The complete nucleotide sequence of a conjugative and integrative plasmid, pSLS, in the thiostrepton-producing Streptomyces laurentii ATCC31255 was determined. The circular DNA molecule was 15,398 bp in length and contained 70.8% G + C content. Computer-assisted analyses indicated that pSLS contained 10 open reading frames (ORFs), orf1 to orf10, located on both strands of pSLS. The orf1 encoded for a predicted protein (200 aa) showed high similarity to TraA protein of non-integrative plasmid pJV1 in Streptomyces phaeochromogenes involved in plasmid transfer and pock-formation. The orf2 coded for a protein of 660 aa that shared homology with TraB proteins encoded by other Streptomyces plasmids. Proteins encoded by orf3 (170 aa), orf4 (408aa) and orf5 (148aa) shared homology with Streptomyces proteins, SpdB1, SpdB2 and SpdB3, respectively, which were also involved in plasmid spreading. The orf8 encoded a polypeptide of 458 aa that shared homology with Int protein of integrative plasmid pSAM2 in Streptomyces ambofacience. This report manifests that pSLS is unique chimeric episomal element that contains gene cluster from non-integrative plasmid and genes for site-specific integration from integrative plasmid.