Nucleotide sequence analysis of small cryptic plasmid pGP2 from Acetobacter estunensis

Abstract

Complete nucleotide sequence of plasmid pGP2 from Acetobacter estunensis GP2 was identified after initial cloning of EcoRI fragment followed by preparation of deletion derivatives. Its size was defined to 2,797 bp and several sites for several restriction enzymes were revealed by DNA sequencing. Sequence analysis predicts three putative open reading frames (ORFs). ORF1 shows significant identity with the bacterial excinuclease α-subunit, ORF2 is a putative replication protein with low similarity with other Acetobacter plasmid's replication proteins, and ORF3 encodes a class B acid phosphatase/phosphotransferase. The replication module comprises a DnaA box like sequence, direct repeats, a potential prokaryotic promoter and a rep gene. The rep module is similar with several θ-replicating, iteron-containing modules from plasmids, suggesting pGP2 replication may follow the same course. Any phenotypic character determinant gene is absent in pGP2, suggesting this plasmid to be cryptic. However, a pGP2 derivative plasmid, containing the putative pGP2 rep region, can replicate and is stably maintained in Acetobacter and Escherichia coli strains; it can also carry foreign DNA fragments. Thus, pGP2-X could serve as a cloning shuttle vector between these bacteria. Prepared deletion derivatives of plasmid pGP2 suggested that Rep protein is essential for plasmid replication in host bacteria. In its natural host, A. estunensis GP2, pGP2 maintains a four-times lower copy number than in E. coli.