FIG. 1.

Substrate for excision repair. The substrate was constructed by ligating six oligonucleotides. The resulting 136-bp duplex contains (6-4) photoproducts at positions +68 and +69 (triangle). The substrate was radiolabeled at either one of two sites (asterisks) by phosphorylating one of the six oligonucleotides with ³²P. Internally labeled substrate was used for excision assays, and terminally labeled substrate was used to detect 5′ incision.