Molecular processing of adenovirus proteins

Late in adenovirus infection, a virus-encoded protease processes several viral structural proteins. The maturation cleavages are a prerequisite for full viral infectivity. The peptide fragment removed during processing is located at the amino end of the major core protein VII. The structure of the precursor peptide sequence was determined by both protein and nucleotide sequencing. Two processing events were elucidated. First, during protein biosynthesis, the initiator methionyl residue is removed and the penultimate seryl residue is acetylated. Second, the resulting NH2-terminal 23-residue fragment is removed during virus assembly. The specificity of the viral endoprotease was investigated by isolating and characterizing another viral proprotein precursor, Pro-VI. The propeptide of VI was also found to be extended at the amino end of the molecule. Comparison of the two propeptide sequences at the cleavage site revealed a consensus amino acid sequence of Gly-Gly-Ala. In addition, there is extensive similarity in the precursor sequences of both proteins. The analogous constitution of the precursor fragments in Pro-VI and Pro-VII suggests that a common mechanism is implicated in controlling the reorganization of VI and VII during virion assembly.