Cleaves viral precursor proteins (pTP, pIIIa, pVI, pVII, pVIII, and pX) inside newly assembled particles giving rise to mature virions. Protease complexed to its cofactor slides along the viral DNA to specifically locate and cleave the viral precursors. Mature virions have a weakened organization compared to the unmature virions, thereby facilitating subsequent uncoating. Without maturation, the particle lacks infectivity and is unable to uncoat. Late in adenovirus infection, in the cytoplasm, may participate in the cytoskeleton destruction. Cleaves host cell cytoskeletal keratins K7 and K18. Cleaves proteins of the adenovirus and its host cell at two consensus sites: -Yaa-Xaa-Gly-Gly-|-Xaa- and -Yaa-Xaa-Gly-Xaa-|-Gly- (in which Yaa is Met, Ile or Leu, and Xaa is any amino acid). Requires DNA and protease cofactor for maximal activation. Inside nascent virions, becomes partially activated by binding to the viral DNA, allowing it to cleave the cofactor that binds to the protease and fully activates it. Actin, like the viral protease cofactor, seems to act as a cofactor in the cleavage of cytokeratin 18 and of actin itself. Interacts with protease cofactor pVI-C; this interaction is necessary for protease activation. Present in about 10 copies per virion. Expressed in the late phase of the viral replicative cycle. All late proteins expressed from the major late promoter are produced by alternative splicing and alternative polyadenylation of the same gene giving rise to non-overlapping ORFs. A leader sequence is present in the N-terminus of all these mRNAs and is recognized by the viral shutoff protein to provide expression although conventional translation via ribosome scanning from the cap has been shut off in the host cell. Belongs to the peptidase C5 family.