Fig. 1. Analysis of replication elongation by molecular combing. (A) Example of labeled molecules with symmetric and asymmetric replication signals. Blue, anti-DNA; green, anti-IdU; red, anti-CldU. (B) Typical examples of labeled molecules obtained from HR proficient (upper panel) or HR-deficient cells (lower panel). (C) Percentage of forks traveling at the indicated speed (kb/minute) in the three HR-deficient cell lines, their respective parental cell line and complemented cell line derivatives. The analysis was performed on 150 DNA fibers with symmetric labeling. The dotted line corresponds to the mean rate in parental V79 or V79-puro cells. We compared the distributions of V79SM, Xrcc2-defective and Xrcc2-complemented cells with the distribution of V79. Consistently, there were no statistical differences between the complemented and the wild-type parental cell lines (P=0.5 for Xrcc2 and P=0.42 for Brca2). By contrast, the distributions between mutant and parental V79 or V79-puro or complemented derivatives were significantly different (P<0.001). There is no statistical difference between the complemented and parental cell lines (P=0.5 for Xrcc2 and P=0.42 for Brca2).