(6-4) PHOTOLYASE - LIGHT-DEPENDENT REPAIR OF DNA-DAMAGE

DNA photolyase represents a phenomenal class of DNA repair enzymes in that it harvests the light energy to repair DNA lesions caused by ultr aviolet light. Mother Nature evolves two types of photolyases, one spe cific for repairing cyclobutane pyrimidine dimers and the other for py rimidine-(6-4)-pyrimidone photoproducts. Together, these two kinds of DNA photolesions account for the majority of ultraviolet light-induced DNA lesions. So far, the basic chemical steps of the enzyme mechanism of the two classes of photolyases appear to be very similar. Therefor e, it will be very intersting to uncover the determinants of the diffe rent substrate specificity between the two photolyases. In this review , we focus on the discussion of the photolyase specific for repairing pyrimidine-(6-4)-pyrimidone photoproducts mainly because the research of the cyclobutane pyrimidine dimer photolyase has recently been revie wed quite extensively.