(dē-oks'ē-rī'bō-dī-pī-rim'i-dēn fō'tō-lī'ās), An enzyme in yeast that is activated by light, whereupon it can reverse a previous photochemical reaction by cleaving the cyclobutane ring of the thymine dimer. Synonym(s): dipyrimidine photolyase, photoreactivating enzyme