Homology among extra-cryptic DNA bands and the typical plasmids in brazilian Yersina pestis strains

RESUMO

Yersina pestis, the etiologic agent of plague, harbors three well-characterized plasmids pFra (90-110kb), pYV (70kb) and pPst (9.5kb). Furthermore, some extra-cryptic DNA bands have been observed in a number of wild strains from several foci of the world. Additional bands have also been reported in Brazilian strains. Looking for any relationship among these cryptic DNA bands and the three-prototypical plasmids, we analyzed twelve strains displaying different plasmid content. The DNA bands were hybridized by southern blot with probes directed at the genes cafl, lcrV and 'pla' located respectively on the plasmids pFra, pYV and pPst. The probes were constructed by PCR amplification and labeled with digoxigenin. The Pla probe hybridized with its target (pPst) and with bands of about 35 kb suggesting some homology among them. The Cafl probe hybridized with the target (pFra) as well as with higher bands. The LcrV also hybridized with the target (pYV) and both with the bands higher than pFra and the bands between pFra and pYV. These results suggest that the large-cryptic bands could represent some rearrangement, open circular or linearized forms of the pFras and pYV plasmids.