A. Wild-type and Pol β null cells one min after irradiation. B. Time course of XRCC1 recruitment to the site of damage. C. PAR synthesis at the site of induced damage (error bars reflect SEM). Recruitment of XRCC1 is significantly different between the two cell lines at the 5 min time point (p < 0.05, Student's t-test), and the PAR levels are significantly different for the 1, 5, and 10 min time points (p < 0.01, Student's t-test).