From DNA photolyases to photoreceptors regulating biological clocks

UV-C produce specific DNA damage such as pyrimidine dimers. These photolesi ons are repaired by, among others, the DNA photolyases which are blue-light activated enzymes found from cyanophycea to lower mammals. However, photol yases are not present in man and placental mammals. The discovery in 1995 o f a photolyase-like gene in man led to the discovery of mammalian cryptochr omes, homologs of recently discovered plant blue-light photoreceptors and o rthologs of photolyases. Cryptochromes do not repair DNA: in plants, they a re involved am others in growth, flowering and resetting the biological clo ks along with the red-light photoreceptors phytochromes. But It has first b een shown in mammals that they acr in resetting circadian rythms and that t hey are also true components of the,biological clock. Beyond that, the expr ession of both the cryptochromes and the clock genes throughout the body is large: Their role may thus be multiple. leading to major medical applicati ons.