The Trichoderma reesei Cry1 Protein Is a Member of the Cryptochrome/Photolyase Family with 6–4 Photoproduct Repair Activity

Abstract

DNA-photolyases use UV-visible light to repair DNA damage caused by UV radiation. The two major types of DNA damage are cyclobutane pyrimidine dimers (CPD) and 6–4 photoproducts (6-4PP), which are repaired under illumination by CPD and 6–4 photolyases, respectively. Cryptochromes are proteins related to DNA photolyases with strongly reduced or lost DNA repair activity, and have been shown to function as blue-light photoreceptors and to play important roles in circadian rhythms in plants and animals. Both photolyases and cryptochromes belong to the cryptochrome/photolyase family, and are widely distributed in all organisms. Here we describe the characterization of cry1, a member of the cryptochrome/photolyase protein family of the filamentous fungus Trichoderma reesei. We determined that cry1 transcript accumulates when the fungus is exposed to light, and that such accumulation depends on the photoreceptor Blr1 and is modulated by Envoy. Conidia of cry1 mutants show decreased photorepair capacity of DNA damage caused by UV light. In contrast, strains over-expressing Cry1 show increased repair, as compared to the parental strain even in the dark. These observations suggest that Cry1 may be stimulating other systems involved in DNA repair, such as the nucleotide excision repair system. We show that Cry1, heterologously expressed and purified from E. coli, is capable of binding to undamaged and 6-4PP damaged DNA. Photorepair assays in vitro clearly show that Cry1 repairs 6-4PP, but not CPD and Dewar DNA lesions.

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“…Similarly, Trichoderma mutants lacking a 6-4 photolyase are more sensitive to damage provoked by UV irradiation (80). In mutants deleted in both photolyases, it was evident that the two enzymes are required for full repair of DNA damaged when the fungi were irradiated with UV (77,80). In agreement with the observation that UV irradiation produces accumulation of more CPD than 6-4 photoproducts in DNA, the CPD photolyase has a more prominent role in reversion of the photodamaged DNA.…”

“…In Cercospora zeae-maydis, one 6-4 photolyase has been described and was proven to have activity in DNA repair when the fungus was exposed to UV irradiation (79). Similarly, Trichoderma mutants lacking a 6-4 photolyase are more sensitive to damage provoked by UV irradiation (80). In mutants deleted in both photolyases, it was evident that the two enzymes are required for full repair of DNA damaged when the fungi were irradiated with UV (77,80).…”

“…In agreement with the observation that UV irradiation produces accumulation of more CPD than 6-4 photoproducts in DNA, the CPD photolyase has a more prominent role in reversion of the photodamaged DNA. Mutants lacking PHR1 are severely affected, whereas mutants from which the 6-4 photolyase-encoding gene (cry-1) has been deleted lose only around 30% of their photorepair capacity (80). There is evidence pointing to a possible regulatory role of photolyases in other repair systems which do not require light for their activity in repairing photoproducts generated by UV radiation (79,81).…”

“…The cryptochromes/6-4 photolyases of Trichoderma (CRY1 in T. atroviride and T. reesei) form part of the animal sub-family of chryptochromes and 6-4 photolyases and have a COOHterminal extension of 79 amino acids, similar to animal cryptochromes and the recently described 6-4 photolyase of Cercospora zeae-maydis, with roles in development and secondary metabolism in addition to their photolyase activity. cry1 gene expression increases in response to exposure to blue light in both T. atroviride and T. reesei in a BLR-dependent fashion, and the corresponding proteins show photoreactivation activity (80,1313). Nevertheless, it has been suggested that at least in T. reesei CRY1 may have additional regulatory functions (80).…”

“…cry1 gene expression increases in response to exposure to blue light in both T. atroviride and T. reesei in a BLR-dependent fashion, and the corresponding proteins show photoreactivation activity (80,1313). Nevertheless, it has been suggested that at least in T. reesei CRY1 may have additional regulatory functions (80). Another notable difference is that the Trichoderma DASH cryptochromes have a longer COOH terminus than those described in animals, plants, bacteria, and other fungi.…”