ANALYSIS OF LINEAR PLASMID DIMERS IN BORRELIA-BURGDORFERI SENSU LATE ISOLATES - IMPLICATIONS CONCERNING THE POTENTIAL MECHANISM OF LINEAR PLASMID REPLICATION

The Borrelia genome is composed of a linear chromosome and a number of variable circular and linear plasmids. Atypically large linear plasmi ds of 92 to 105 kb have been identified in several Borrelia burgdorfer i sensu late isolates and characterized. These plasmids carry the p27 and ospAB genes, which in other isolates reside on a 50-kb plasmid. He re we demonstrate that these plasmids are dimers of the 50-kb ospAB pl asmid (pAB50). The 94-kb plasmid from isolate VS116, pVS94, was an exc eption and did not hybridize with any plasmid gene probes. When this p lasmid was used as a probe, homologous sequences in other isolates wer e not detected, suggesting that it is unique to isolate VS116. These a nalyses provide insight into the mechanism of linear plasmid replicati on and the mechanisms by which plasmid variability can arise.