The nuclease activity of Dna2 is required for both HR-dependent DSB repair and Rad51-focus formation.

<p>(A) Cells carrying the indicated genotypes were incubated with doxycycline for 24 hours, exposed to 2 Gy γ-rays, and analyzed for chromosomal aberrations in mitotic cells 3 hours after the irradiation. Error bars represent standard deviation calculated from three independent experiments. (B) Top: schematic of chromosome analysis for detecting olaparib-induced breaks. Bottom: Percentage of chromosomal aberrations in mitotic cells carring the indicated genotypes. Error bars represent standard deviation calculated from three independent experiments. At least 100 cells were counted for each cell line. (C) The indicated genotypes were incubated with doxycycline for 24 hours, exposed to IR, and then immunostained with anti-Rad51 antibody at the indicated time post-IR. The average number of Rad51 foci per cell was calculated from three independent experiments. At least 100 cells were counted for each cell line. The representative images are shown in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0124495#pone.0124495.s003" target="_blank">S3A Fig</a>. Error bars were plotted for standard deviation (SD), and <i>p</i>-values were calculated using Mann-Whitney U-test. Asterisks indicate a p-value of <0.01.