Nucleotide sequence analysis of pOg32, a cryptic plasmid from Leuconostoc oenos

Analysis of the nucleotide sequence of Leuconostoc oenos plasmid pOg32 (2544 bp) revealed three open reading frames (ORFs) in one of the DNA strands preceded by putative promoters and ribosome binding sites. ORF1 corresponded to a polypeptide similar to the replication proteins (Rep) of pT181 plasmid family. A nucleotide sequence like the double strand origin (DSO) of the same plasmid family was found inside the presumptive rep gene. ORF2 is capable of encoding a protein resembling the recombination enzyme (Pre) of two lactobacilli plasmids. Immediately upstream of the presumed pre gene, a sequence similar to the consensus RSA regions of those plasmids was encountered. Between ORF3 and ORF1, a sequence comparable to the RSB consensus region of the single strand origin ssoA was detected. The putative RSB region was located at the 3'-end of an imperfect palindrome which may be a single stranded origin. The described features, common to other small plasmids of Gram-positive bacteria, suggest that pOg32 replicates by the rolling circle mechanism. The amino acid sequence encoded by ORF3 was not similar to any known protein.