Marker rescue by a homologous recipient plasmid during transformation of gonococci by a hybrid Pcr plasmid.

A 42-kilobase hybrid Pcr plasmid (pFA14) was formed when the naturally occurring 7.2-kilobase Pcr plasmid pFA3 was introduced by transformation into a competent gonococcal recipient containing the 36-kilobase conjugative plasmid pFA2 (Sox et al., J. Bacteriol. 138:510-518). Analysis of the structure of pFA14 showed that it was a stable recombinant between pFA3 and pFA2. The transformation efficiency of pFA14 was increased 300- to 10,000-fold by the presence in isogenic recipients of the homologous plasmid pFA2. The presence of a homologous plasmid in the recipient also markedly increased the likelihood of recovery of intact donor-size Pcr plasmids in the transformants. The presence of pFA2 had no effect on the competence of piliated or nonpiliated gonococci for transformation by either linear chromosomal DNA or a nonhomologous Pcr plasmid. Increased transformation efficiency of the hybrid Pcr plasmid pFA14 may have been due to recombination between the nicked or linearized donor plasmid and the homologous recipient plasmid (marker rescue).