Involved in repair of UV radiation-induced DNA damage. Catalyzes the light-dependent monomerization (300-600 nm) of cyclobutyl pyrimidine dimers (in cis-syn configuration), which are formed between adjacent bases on the same DNA strand upon exposure to ultraviolet radiation. cyclobutadipyrimidine (in DNA) = 2 pyrimidine residues (in DNA). Binds 1 FAD per subunit. Binds 1 5,10-methenyltetrahydrofolate (MTHF) non-covalently per subunit. The occupancy is 0.2. Usually had equal molar flavin and folate. Monomer. Belongs to the DNA photolyase class-1 family.