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It is unclear how, or to what extent, baculovirus DNA that has been damaged by ultraviolet (UV) light is repaired during infection and replication. In our previous study, expression of Bombyx mori nucleopolyhedrovirus (BmNPV) ORF Bm65, a homolog of Autographa californica multiple nucleopolyhedrovirus (AcMNPV) ac79, correlated with decreased inactivation of virus by UV irradiation. In the current study, we accumulated more evidence pointing to a role for Bm65 in repair of UV-induced DNA damage. The localization of Bm65 was studied using enhanced green fluorescent protein (EGFP) fusion constructs expressed in BmN cells transfected with a Bm65 expression plasmid. The results indicate that Bm65-EGFP accumulates in the nucleus. A host cell reactivation assay showed that Bm65 significantly increased the expression of UV-damaged mCherry reporter gene. An assay measuring cyclobutane pyrimidine dimers (CPDs) in UV-irradiated BmN cells found that CPD quantity was decreased in cells transfected with a Bm65 expression plasmid. We also showed that after UVC treatment, the viability of Bm65-transfected cells was higher than that of egfp-transfected cells. These results suggest that Bm65 may be involved in the repair of baculovirus DNA that has been damaged by UV light. [ABSTRACT FROM AUTHOR]

[Display omitted] Solar ultraviolet radiation (UV) can cause DNA damage in microorganisms. Flap endonuclease 1 (FEN1) is a structure-specific nuclease and plays important roles in DNA replication and repair. At present, the properties and functions of FEN1 have not been characterized in detail in invertebrates such as Bombyx mori. In this study, Bombyx mori FEN1 (BmFEN1) was expressed in E. coli, and was shown to have nuclease activity that nonspecifically cleaved DNA in vitro. However, inside the cell, BmFEN1 did not cleave DNA randomly. Truncated BmFEN1 missing the nuclear localization signal (346–380 aa) still had the nuclease activity, but was no longer precisely localized to the sites of UV-induced DNA damage. It was further found that BmFEN1 favored the faster repair of UV-damaged DNA. The present study will provide a reference for further understanding the functions of BmFEN1 and UV-induced DNA damage repair mechanisms in insects. [ABSTRACT FROM AUTHOR]