Figure 1.

p21 inhibits interstrand crosslink-induced DNA synthesis. (A) All reactions contained HeLa cell extracts at 2.5 mg/ml and other components as described previously (1). p21 was preincubated with the HeLa cell extracts on ice for 30 min prior to addition of the other components. The reactions were subsequently incubated for 3 h at 28°C and processed as previously described (1). The addition of p21 was as follows: lanes 1 and 2, none; lane 3, 0.57 µM; lane 4, 1.14 µM; lane 5, 2.29 µM. Lane 1 contains the DT and CT plasmids and all other lanes contain the DT and CLT plasmids. Both the autoradiogram and ethidium bromide staining of the gel are shown. (B) Quantitation of the experiment shown in (A). All quantitations derived from autoradiograms were normalized for plasmid recovery as measured from the ethidium bromide stained gels. Open circle, DT plasmid; closed circle, CLT plasmid.