Definition for Photolyase
From Biology Forums Dictionary
Photolyases are DNA repair enzymes that repair damage caused by exposure to ultraviolet light. This enzyme mechanism requires visible light, preferentially from the violet/blue end of the spectrum, and is known as photoreactivation.
Photolyase is a phylogenetically old enzyme which is present and functional in many species, from the bacteria to the fungi to the animals. However it is no longer working in humans and other placental mammals who instead rely on the less efficient nucleotide excision repair mechanism.
Photolyases bind complementary DNA strands and break certain types of pyrimidine dimers that arise when a pair of thymine or cytosine bases on the same strand of DNA become covalently linked. These dimers result in a 'bulge' of the DNA structure, referred to as a lesion. The more common covalent linkage involves the formation of a cyclobutane bridge. Photolyases have a high affinity for these lesions and reversibly bind and convert them back to the original bases.