Photolyase

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Photolyase is an enzyme that binds complementary DNA strands and breaks pyrimidine dimers that are typically caused by exposure to ultraviolet light. Pyrimidine dimers occur when a pair of thymine bases or cytosine bases on the same strand of DNA bind together, resulting in a 'bulge' of the DNA structure referred to as a lesion. Photolyase has a high affinity for these lesions in the DNA and will reversibly bind and split the dimer using light-energy. This enzyme only functions as a DNA repair mechanism when visible light is available (preferentially from the violet/blue end of the spectrum). This process is also known as photoreactivation.

This enzyme is a flavoprotein and acts by electron transfer. In this protein the FADH molecule acts as the electron donor and the pyrmidine dimer acts as the electron acceptor. Photolyase is present and functional in prokaryotes, is present in lower eukaryotes (as yeast) where it is thought to have a minor role, and it has not been found in human cells.