On the intracellular transport and the nuclear association of human cytomegalovirus structural proteins.

In cells productively infected with human cytomegalovirus (HCMV) AD169, large amounts of two viral proteins, the 150K major capsid and the 68K major matrix proteins, are continuously produced during the late phase of infection. In the present study, the mechanism for the intracellular transport of the 150K and 68K proteins was investigated. Infected cells were labelled for 30 min at 72 h post-infection with [35S]methionine, chased for various periods of time at 37 degrees C, and fractionated into cytoplasmic and nuclear fractions. Immediately after 30 min of labelling, the 68K protein was already associated with the nuclear fraction. In contrast, the major proportion of the 150K protein remained in the cytoplasm for more than 1 h; the migration of the 150K protein was much slower than that of the 68K protein. Both the 150K and the 68K proteins were associated with the perinuclear cytoskeletal fraction in the process of migration. After migration into the nucleus, these proteins were resistant to extraction with DNase and high salt, indicating that they were associated with the nuclear skeleton (nuclear matrix). Effects of various inhibitors on the migration of the 150K protein showed that cycloheximide inhibited the transport of the 150K protein, but other inhibitors such as arabinosyl cytosine, cytochalasin D, colchicine or sodium azide did not. The results suggest that the cytoskeletal structure may play a role in the intracellular transport of HCMV structural proteins from the cytoplasm into the nucleus.