Involved in viral genome packaging through its interaction with packaging proteins 1 and 2. After proteolytic cleavage by adenovirus protease, L1 52/55k protein is removed from the capsid during viral maturation. Part of the genome packaging complex composed of packaging proteins 1, 2 and 3; this complex specifically binds to the packaging sequence on the left end of viral genomic DNA and performs packaging of the viral genome. Interacts with hexon-linking protein IIIa; this interaction is required to promote correct genome packaging. Nuclear protein present in empty capsids and assembly intermediates. Expressed in the early phase and late phase of the viral replicative cycle. Cleaved at different sites by the viral protease during virion maturation. 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 adenoviridae packaging protein 3 family.