Deletion of the AcMNPV core gene ac109 results in budded virions that are non-infectious

Autographa californica multiple nucleopolyhedrovirus (AcMNPV) ac109 is a core gene and its function in the virus life cycle is unknown. To determine its role in the baculovirus life cycle, we used the AcMNPV bacmid system to generate an ac109 deletion virus (vAc109KO). Fluorescence and light microscopy showed that transfection of vAc109KO results in a single-cell infection phenotype. Viral DNA replication is unaffected and the development of occlusion bodies in vAc109KO-transfected cells evidenced progression to the very late phases of viral infection. Western blot and confocal immunofluorescence analysis showed that AC109 is expressed in the cytoplasm and nucleus throughout infection. In addition, AC109 is a structural protein as it was detected in both budded virus (BV) and occlusion derived virus in both the envelope and nucleocapsid fractions. Titration assays by qPCR and TCID50 showed that vAc109KO produced BV but the virions are non-infectious. The vAc109KO BV were indistinguishable from the BV of repaired and wild type control viruses as determined by negative staining and electron microscopy.