Regulatory Mechanisms, Protein Expression and Biological Activity of Photolyase Gene from Spodoptera littoralis Granulovirus Genome

One of the most important factor that affects the efficient using of baculoviruses as a biopesticide is their sensitivity to UV irradiation. In this study, a photolyase gene (phr) of 1.4 kbp DNA fragment was cloned and characterized from Spodoptera littoralis granulovirus, an Egyptian isolate (SpliGV-EG1). A sequence of 466 amino acid were deduced when the gene was completely sequenced with a predicted molecular mass of ~ 55 kDa. Transcriptional regulation analyses revealed that phr transcripts were detected early at 6-h post-infection (hpi) and remained detectable until 72 hpi, suggesting their transcriptional regulation from a putative early promoter motif. An approximately ~ 55 kDa protein fragment was expressed from phr-induced bacterial culture and detected by SDS-PAGE and western blotting. In addition, direct exposure to UV irradiation resulted in a twofold decrease in SpliGV-EG1 occlusion bodies activation compared with Spodoptera littoralis nucleopolyhedrovirus (SpliNPV) occlusion bodies which decreased with about 129-fold after exposure to UV irradiation based on median lethal concentration value (LC50). The obtained results suggested that the presence of photolyase gene possibly alters the inactivation of SpliGV-EG1-occluded bodies by UV irradiation. These results support the role and application of the photolyase protein to improve the damaged DNA repair mechanism as well as resistance of SpliGV to UV light inactivation.