Characterization of two small cryptic plasmids from Pseudomonas sp. strain S-47

Two small cryptic plasmids, p47L and p47S, identified in Pseudomonas sp. S-47 were characterized by determination of DNA sequences and physical and functional maps. They are 3084 and 1782 bp in length, respectively, with GC contents of 63.55 and 65.21%. The detection of single-strand DNAs of both plasmids indicates that they replicate by a rolling-circle mechanism. The deduced polypeptide encoded by the rep gene of p47L is homologous with Rep proteins of plasmids belonging to the pIJ101/pJV1 family, which are known to replicate by the rolling-circle mechanism. Despite containing a homologous signature with Rep proteins of rolling-circle replicating (RCR) plasmids in the pT181 family, the Rep of p47S lacks significant homology with Rep proteins of this family and is missing a region similar to the family's replication origin (dso). Based on the rep sequence comparisons, p47L falls into a previously defined plasmid family whereas p47S defines a new family of RCR plasmid.