Restoration of DNA repair in UV-sensitive Chinese hamster ovary cell by the denV gene from bacteriophage T4.

Abstract

The denV gene of bacteriophage T4, which is the principal determinant of resistance to ultraviolet light (UV) on the T4 genome,1 codes for endonuclease V, a 16,000 dalton protein possessing two distinct enzymatic activities which can act sequentially to initiate repair of pyrimidine dimers. A pyrimidine dimer-DNA glycosylase activity first cleaves one of the two bonds attaching the pyrimidine dimer to the DNA backbone, leaving an apyrimidinic site, and an AP-endonuclease activity associated with the same polypeptide subsequently introduces a single-strand break at this site.2,3 like the very similar enzyme from Micrococcus luteus, described by R. Grafstrom elsewhere in this volume, endonuclease V leaves residual damage products on both sides of the single-strand break, which presumably must be removed by other enzymes before repair synthesis can take place. The phage T4 and M. luteus enzymes catalyze a base excision process and are in this respect distinguishable from other known pyrimidine dimer repair systems, which proceed via a nucleotide excision repair mechanism. In spite of these differences, experiments with permeabilized cells have shown that endonuclease V is capable of restoring excision repair of UV damage not only in repair-deficient E. coli 4 but also in human fibroblasts from patients with the heritable UV repair disorder xeroderma pigmentosum.5,6 Thus the denV gene is an interesting candidate for genetic correction of UV repair deficiency in both prokaryotic and eukaryotic cells.