Fig. (5) Crystal structure of A. nidulans photolyase with different DNAs (repaired CPD-like substrate). The CPD-like substrates are (11) and (10) configurations, respectively. The first substrate (11) is left (bottom), the second (10) is right (bottom). The electron transfer causes the splitting of the dimer into an original shape, so it becomes an electron donor. The electron transfers back to a flavin which transforms the CPD-like substrate into a required nucleoside pair (from FADH^o to FADH^-). A positively charged flavin is FADH^o, a neutral flavin is FADH^-.