Complete nucleotide sequence and characterization of pSNA1 from pimaricin-producing Streptomyces natalensis that replicates by a rolling circle mechanism

A cryptic plasmid, pSNA1, has been identified in the pimaricin-producing St reptomyces natalensis strain ATCC 27448. pSNA1 has been mapped with restric tion endonucleases and its complete nucleotide sequence was determined. The circular DNA molecule is 9367 bp in length and has a 71.3% G+C content. It s estimated copy number is 30. Analysis of the sequence and codon preferenc es indicated that pSNA1 contains seven open reading frames [encoding peptid es larger than 90 amino acid (aa) residues], ORF 1 to ORF 7, located on bot h strands of pSNA1. ORF 3 codes for a protein (476 aa) that shows high sequ ence similarity to replication-associated proteins in Streptomyces plasmids known to replicate via the rolling circle mechanism. Accumulation of singl e-strand intermediates further indicates that pSNA1 replicates via the roll ing circle replication model. ORF 1 encodes a polypeptide of 246 aa that sh ares homology with KorA proteins encoded by other streptomycete plasmids. O RF 4 (SpdA) codes for a protein (161 aa) possibly involved in intramycelial plasmid transfer. Protein encoded by ORF 2 (309 aa) shares homology with a Streptomyces protein (SpdB2) also involved in plasmid spreading, (C) 2000 Academic Press.