Plays a role at the late stage in the encapsidation of viral DNA, assuring correct genome cleavage and presumably stabilizing capsids that contain full-lengtht viral genomes. Located on the external vertices of the T=16 icosahedric capsid, may bind together the tegument and the capsid through interaction with large tegument protein U31 (By similarity). Heterodimerizes with packaging protein U64. Interacts with major capsid protein U57 and triplex capsid protein U29, essentially at the pentamer vertices. May interact with large tegument protein U31 (By similarity). Belongs to the herpesviridae UL25 family.