Removal of UV light-induced pyrimidine-pyrimidone(6-4) products from Escherichia coli DNA requires the uvrA, uvrB, and urvC gene products.

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Abstract
UV light induces the formation of cyclobutane pyrimidine dimers and pyrimidone(6-4) photoproducts in cellular DNA. In E. coli, the uvrA, uvrB and uvrC gene are necessary for excision of cyclobutane dimers. To determine whether the uvrABC gene products are required for (6-4) product removal from DNA, a sensitive HPLC [high performance liquid chromatography] assay was developed that allows the separation and quantitation of both types of photoproducts. Both the .**GRAPHIC**. cyclobutane dimer and the T-C(6-4) product were completely removed from the DNA after 2 h of repair in a wild-type strain. Both products were also removed in the wild-type strain in the presence of chloramphenicol, an inhibitor of protein synthesis. No decrease in the amount of .**GRAPHIC**. cyclobutane dimer or of T-C(6-4) products was observed in strains that were deficient in any of the 3 uvr gene products under similar conditions. The urvABC enzyme complex apparently is required for excision of (6-4) photoproducts from E. coli DNA.