FIG. 5.

Further characterization of the iap/ibp locus arrangement and demonstration that this locus can exist as circular intermediates that could be transposition intermediates. Based upon sequencing of a long-range PCR product connecting dcm to the iap/ibp locus in NCIB10748 (not shown), an overlapping PCR assay was designed and applied to the eight surveyed type E isolates. Results for NCIB10748 are shown in panel A; similar results were also observed with the other seven isolates. Panel B shows results from a PCR assay that used primer sets that amplify products from the iap/ibp locus of NCIB10748 when this locus is present in a small circular form but not in a linear form. The primer sets used are R1 (primers L1-R and P8-F), R2 (L1-R and L1-F), R3 (P1-R and L1-F), and R4 (P1-R and P8-F); locations of primers are shown in panel A. Panel C shows the expected products from small circular forms containing IS1151-2-ibp-iap-silent cpe sequences or ibp-iap-silent cpe sequences. The identity of these products was confirmed by DNA sequencing.