Similarity of minus origins of replication and flanking open reading frames of plasmids pUB110, pTB913 and pMV158

Abstract

Plasmids pMV 158 and pTB913, originating from Streptococcus agalactiae and a thermophilic Bacillus respectively, were sequenced to completion. Both contained a BA3-type minus origin of replication and an RS_A-site, believed to constitute a site-specific recombination site. These two regions were more than 99% homologous to the corresponding regions of the Staphylococcus aureus plasmid pUB110. Deleting the BA3-type minus origin resulted in the accumulation of a considerable amount of single-stranded DNA, both in L.lactis subsp. lactis and B.subtilis, indicating that this minus origin was functional in both bacterial species. Like pUB110, both plasmids contained an open reading frame encoding a putative plasmid recombinalion enzyme (Pre protein), which was located downstream of the RS_A-site. On the basis of sequence comparisons between pUB110, pMV158, pTB913, pT181, pE194, pNE131 and pT48 two distinct families of RS_A-sites and Pre proteins could be distinguished