The measurement of DNA excision repair activity in vitro, originally developed by Wood and co-workers (1 ), utilizes transcriptionally active protein extracts obtained from mammalian cells by the method of Manley et al. (2 ) (seeChapter 29 ). Nucleotide excision repair (NER), which requires more than 20 proteins in vitro, can process a large variety of lesions according to the following mechanism:
| 1. | Recognition of the DNA lesion. |
| 2. | Incision on both sides of the lesion. |
| 3. | Excision of the damaged oligonucleotide. |
| 4. | DNA polymerization and ligation. |
