FIG. 2.

Identification and quantification of cointegration and excision events in wild-type NGR234 and in the derivative CFNX416. (A) Schematic representation of cointegration and excision between two replicons (a and b) sharing homologous repeats (⌂, ). The use of FP and RP from the same replicon reveals the wild-type structure. A combination of FP of replicon a and RP of replicon b or vice versa allows the detection of the recombinant bands (, ) generated in the cointegration; reversion is revealed by detecting the original structure with primers belonging to each of the replicons. (B) PCR products monitored by agarose gel electrophoresis and staining with ethidium bromide. PCR assays were performed at a different cycle of reactions (indicated at the bottom of the lanes). Different primers were used to detect the original or recombinant PCR products. The quantification was carried out by comparing the number of PCR cycles necessary to produce a certain amount of PCR product as indicated in Materials and Methods. Chr, chromosome; mega, megaplasmid pNGR234b; and sym, symbiotic plasmid pNGR234a.