FIG. 4.

Evidence for unidirectional recombination of silent vls cassette segments into vlsE. (A) Diagram of locations of oligonucleotide probes in vlsE and the silent vls cassettes in the parental strain B31-5A3 and its derivative strains M1e4A and M1e4C. (B) Hybridization of oligonucleotide probe R4232 with the blots of restriction enzyme-digested plasmid DNA preparations from B31-5A3, M1e4A, and M1e4C. In all lanes, the probe hybridized to a single band corresponding to a region containing the silent cassette vls11 in both strains B31-5A3 and M1e4A. However, for strain M1e4C, two bands were detected in each digest that corresponded to the vlsE region with the second band (arrows). The molecular sizes of DNA bands are indicated in kilobases on the left side.