A bifunctional CPD/(6-4)- photolyase from the cyanobacteria Synechococcus sp. PCC 7335 constitutes an UV-B inducible operon: new insights into photolyases phylogenetic evolution

Abstract

Photosynthetic organisms are continuously exposed to solar ultraviolet radiation-B (UV-B) because of their autotrophic lifestyle. UV-B provokes DNA damages, as cyclobutane pyrimidine dimers (CPD) or pyrimidine (6-4) pyrimidone photoproducts (6-4 PPs). The cryptochrome/ photolyase family (CPF) comprises flavoproteins that are able to bind damaged or undamaged DNA. Photolyases (PHRs) are enzymes that repair either CPDs or 6-4 PPs. A natural bifunctional CPD/(6-4)- PHR (PhrSph98) was recently isolated from the UV-resistant bacteria Sphingomonas UV9. In this work, phylogenetic studies of bifunctional CPD/(6-4)- photolyases and its evolutionary relationship with other CPF members were performed. Amino acids involved in electron transfer and binding to FAD cofactor and DNA lesions were conserved in proteins from proteobacteria, planctomycete, bacteroidete, acidobacteria and cyanobacteria clades. Genome analysis revealed that the cyanobacteria Synechococcus sp. PCC 7335 encodes a two-gene assembly operon coding for a PHR and a bifunctional CPD/(6-4)- PHR. Operon structure was validated by RT-qPCR analysis and the polycistronic transcript accumulated after 15 minutes of UV-B irradiation. Conservation of structure and evolution is discussed. This is the first report of an UV-B inducible PHRs operon which encodes a CPD/(6-4)- photolyase with putative bifunctional role in the repair of CPDs and 6-4 PPs damages in oxygenic photosynthetic organisms.