Proteolytic cleavage of bovine adenovirus 3-encoded pVIII

Proteolytic maturation involving cleavage of one nonstructural and six structural precursor proteins including pVIII by adenovirus protease is an important aspect of the adenovirus life cycle. The pVIII encoded by bovine adenovirus 3 (BAdV-3) is a protein of 216 amino acids and contains two potential protease cleavage sites. Here, we report that BAdV-3 pVIII is cleaved by adenovirus protease at both potential consensus protease cleavage sites. Usage of at least one cleavage site appears essential for the production of progeny BAdV-3 virions as glycine-to-alanine mutation of both protease cleavage sites appears lethal for the production of progeny virions. However, mutation of a single protease cleavage site of BAdV-3 pVIII significantly affects the efficient production of infectious progeny virions. Further analysis revealed no significant defect in endosome escape, genome replication, capsid formation, and virus assembly. Interestingly, cleavage of pVIII at both potential cleavage sites appears essential for the production of stable BAdV-3 virions as BAdV-3 expressing pVIII containing a glycine-to-alanine mutation of either of the potential cleavage sites is thermolabile, and this mutation leads to the production of noninfectious virions.