RAD51-dependent and independent BES repair and antigenic variation.

<p>(A) Nuclei with RAD51 foci were scored following a DSB at a chromosome-internal locus (Control) or at the active or silent BES. I-<i>Sce</i>I expression was induced for 12 h. n = 200 for each bar. Error bars for BES-break strains, SD. The inset shows a representative example of a nuclear RAD51 focus, red; DNA, blue; scale-bar, 5 µm. (B) Western blot analysis of <i>rad51</i> null strains, the Coomassie panels serve as loading controls. (C) Clonogenic assays. <i>rad51</i> null strains were distributed in 96-well plates under I-<i>Sce</i>I inducing conditions. Survivors were assessed after 7 days. Two independent clones were assayed in triplicate plates for each strain. A wild-type control displayed close to 100% survival (data not shown). Error bars, SD. *, <i>P</i><0.05 based on Student's t-test. (D). PCR assays were used to check for the presence of the <i>ESAG1</i> gene in VSG^up<i>rad51</i>-null survivors following I-<i>Sce</i>I induction (n = 20).