Photobiological significance of DNA photolgase/Blue-light photoreceptor family

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We report isolation of a Xenopus laevis (6-4)photolyase gene, and show that the (6-4)photolyase binds noncovalently to stoichiometric amounts of FAD.Xenopus (6-4) photolyase binds with high affinity to DNA bearing a (6-4) photoproduct and repairs it in a light-dependent reaction. To clarify its repair mechanism of (6-4) photolyase, we determined its binding and catalytic properties using synthetic DNA substrate which carries a photoproduct at a single location. The (6-4)photolyase binds to T[6-4]T in double stranded DNA with high affinity (kD = 10_<-9>) and to T[6-4]T in single stranded DNA and T[Dewar]T in double- and single-stranded DNA although with slightly lower affinity (k_D = -2 x 10_<-8>). Majority of the T[6-4]T (6-4) photolyase-complex dissociates very slowly (koff = 2.9 x 10_<-5 S-1>). Its absolute action spectrum without a second chromophore in the 350-600 nm region closely matches the absorption spectrum of the enzyme. The quantum yield (f) of repair is approximately 0.11. … More The fully reduced form (E-FADH-) of (6-4)photolyase is catalytically active. Direct analysis of the photoreactivated product showed that (6-4) photolyase restores the original pyrimidines. These findings demonstrate that CPD photolyase and (6-4)photolyase are quite similar, but they are different with regard to the binding properties.Light is the major environmental signal for the entrainment of circadian rhythms. Light signals can entrain these rhythms by shifting their phases. However, little is known about the molecular mechanism for the perception and transduction of the light signal. The members of the photolyase/cryptochrome family contain flavin adenine dinucleotide (FAD) as chromophore and are involved in two diverse functions, DNA repair and photoreception of environmental light signals. We report the cloning of a new member of this family, dcry, from Drosophila. Northern blot analysis shows that this gene is expressed in various tissues. . The dcry mRNA is expressed in a circadian manner in adult heads, while such rhythmic fluctuation is abolished in the clock-defective per0 and tim0 mutants. The circadian expression damps in constant darkness. Over-expression of the dcry gene alters the light-induced phase delay in the locomotor activity rhythms of flies. These results suggest that DCRY is a circadian photoreceptor and its expression is regulated by circadian clock genes.. Less