Autographa californica multiple nucleopolyhedrovirus ac142, a core gene that is essential for BV production and ODV envelopment

Autographa californica multiple nucleopolyhedrovirus (AcMNPV) ac142 is a baculovirus core gene and encodes a protein previously shown to associate with occlusion-derived virus (ODV). To determine its role in the baculovirus life cycle, we used the AcMNPV bacmid system to generate an ac142 deletion virus (AcBACac142KO-PH-GFP). Fluorescence and light microscopy revealed that AcBACac142KO-PH-GFP exhibits a single-cell infection phenotype. Titration assays and Western blot confirmed that AcBACac142KO-PH-GFP is unable to produce budded virus (BV). However, viral DNA replication is unaffected and the development of occlusion bodies in AcBACac142KO-PH-GFP-transfected cells evidenced progression to very late phases of the viral infection. Western blot analysis showed that AC142 is expressed in the cytoplasm and nucleus throughout infection and that it is a structural component of BV and ODV which localizes to nucleocapsids. Electron microscopy indicates that ac142 is required for nucleocapsid envelopment to form ODV and their subsequent occlusion, a fundamental process to all baculoviruses.