The viral ubiquitin gene of Autographa californica nuclear polyhedrosis virus is not essential for viral replication.

The baculovirus Autographa californica nuclear polyhedrosis virus (AcNPV) encodes a protein with significant homology to ubiquitin. To study the role of viral ubiquitin in infection, a recombinant virus was constructed with a frameshift mutation within the coding sequence of the viral ubiquitin gene, v-ubi. This recombinant, named Vubi-FS, was viable, indicating that viral ubiquitin is not essential for replication in tissue culture. However, the yields of infectious budded virus were decreased 5- to 10-fold in single step growth curves, and the production of total budded virions was reduced to a similar extent. The mutant virus particles contained the phospholipid-modified form of ubiquitin (Pt-Ub), and amino acid sequence analysis revealed that only host ubiquitin was packaged into virions. Together, these results suggest that viral ubiquitin is a nonessential protein that may confer a slight growth advantage under certain conditions.