The Autographa californica Multiple Nucleopolyhedrovirus Gene Is Required for Efficient Nuclear Egress of Nucleocapsids and Is Essential for Virulence.

Alphabaculoviruses are lepidopteran-specific nucleopolyhedroviruses that replicate within the nucleus; however, the anterograde transport of the nucleocapsids of these viruses, which is an obligatory step for progeny virion production, is not well understood. In the present study, a unique gene with unknown function, namely, the Autographa californica multiple nucleopolyhedrovirus (AcMNPV) gene, was found to be required for efficient nuclear egress of AcMNPV nucleocapsids. Our results indicate that is a late gene, and Ac51 protein was detectable from 24 to 72 h postinfection using an antibody raised against Ac51. Ac51 is distributed in both the cytoplasm and nuclei of infected cells. Upon deletion, budded virion (BV) production by 96 h posttransfection was reduced by approximately 1,000-fold compared with that of wild-type AcMNPV. Neither viral DNA synthesis nor viral gene expression was affected. Ac51 was demonstrated to be a nucleocapsid protein of BVs, and deletion did not interrupt nucleocapsid assembly and occlusion-derived virion (ODV) formation. However, BV production in the supernatants of transfected cells during a viral life cycle was substantially decreased when was deleted. Further analysis showed that, compared with wild-type AcMNPV, deletion decreased nucleocapsid egress, while the numbers of nucleocapsids in the nuclei were comparable. Deletion of also eliminated the virulence of AcMNPV Taken together, our results support the conclusion that plays an important role in the nuclear egress of nucleocapsids during BV formation and is essential for the virulence of AcMNPV.