PHOTOREACTIVATING ENZYME FOR (6-4)PHOTOPRODUCTS IN CULTURED GOLDFISH CELLS

We previously reported that when cultured goldfish cells are illuminat ed with fluorescent light, photorepair ability for both cyclobutane py rimidine dimers and (6.4) photoproducts increased. In the present stud y, it was found that the duration of the induced photorepair ability f or cyclobutane pyrimidine dimers was longer than that for (6.4) photop roducts, suggesting the presence of different photolyases for repair o f these two major forms of DNA damage. A gel shift assay was then perf ormed to show the presence of protein(s) binding to (6-4) photoproduct s and its dissociation from (6-4) photoproducts under fluorescent ligh t illumination, in addition, at 8 h after fluorescent light illuminati on of the cell, the binding of protein(s) to (6-4) photoproducts incre ased. The restriction enzymes that have recognition sites containing T T or TC sequences failed to digest the UV-irradiated DNA photoreactiva ted by using Escherichia coli photolyase for cyclobutane pyrimidine di mers, indicating that restriction enzymes could not function because ( 6-4) photoproducts remained in recognition sites. But, when UV-irradia ted DNA depleted of cyclobutane pyrimidine dimers was incubated with e xtract of cultured goldfish cells under fluorescent Light illumination , it was digested with those restriction enzymes. These results sugges ted the presence of (6-4) photolyase in cultured goldfish cells as in Drosophila, Xenopus and Crotalus.