Assessment of DSB formation during repair. ³²P-labeled (*) duplexes were incubated with 20 μg of proteins from whole cell extracts at 37°C for various period of time and separated on 12% nondenaturing polyacrylamide gels. (i) Representative polyacrylamide gels demonstrating DSB formation following incubation of duplexes AP/AP and MDS-1 with yeast whole-cell extract for various periods of time. (ii) rates of DSB induction by cell extract in duplexes U/U, AP/AP, AP/U, U/AP, MDS-2, MDS-1 and IMDS-oG4/hU. Two different cell extracts were used. Data represent the means of at least two independent experiments for each extract.