Localization of human cytomegalovirus structural proteins to the nuclear matrix of infected human fibroblasts

The intranuclear assembly of herpesvirus subviral particles remains an incompletely understood process. Previous studies have described the nuclear localization of capsid and tegument proteins as well as intranuclear tegumentation of capsid-like particles. The temporally and spatially regulated replication of viral DNA suggests that assembly may also be regulated by compartmentalization of structural proteins. We have investigated the intranuclear location of several structural and nonstructural proteins of human cytomegalovirus (HCMV). Tegument components including pp65 (ppUL83) and ppUL69 and capsid components including the major capsid protein (pUL86) and the small capsid protein (pUL48/49) were retained within the nuclear matrix (NM), whereas the immediate-early regulatory proteins IE-1 and IE-2 were present in the soluble nuclear fraction. The association of pp65 with the NM resisted washes with 1 M guanidine hydrochloride, and direct binding to the NM could be demonstrated by far-Western blotting. Furthermore, pp65 exhibited accumulation along the nuclear periphery and in far-Western analysis bound to proteins which comigrated with proteins of the size of nuclear lamins. A direct interaction between pp65 and lamins was demonstrated by coprecipitation of lamins in immune complexes containing pp65. Together, our findings provide evidence that major virion structural proteins localized to a nuclear compartment, the NM, during permissive infection of human fibroblasts.