Interacts with the viral DNA and aids in tightly condensing it within the capsid. Cleavage of pre-core protein X may serve to partially relax this structure within the mature virion prior to its entry into the nucleus (By similarity). Interacts with the core-capsid bridging protein; this interaction bridges the virus core to the capsid. Excluded from adenovirus DNA-binding protein (DBP)-rich replication centers in adenovirus-infected cells. Located inside the capsid in association with the viral DNA (core). Present in about 126-160 copies per virion. Excluded from adenovirus DNA-binding protein (DBP)-rich replication centers in adenovirus-infected cells (By similarity). Expressed in the late phase of the viral replicative cycle. Cleaved by the viral protease during virion maturation to form the mature protein. 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 (By similarity). Belongs to the adenoviridae core protein X family.