ASSEMBLONS - NUCLEAR-STRUCTURES DEFINED BY AGGREGATION OF IMMATURE CAPSIDS AND SOME TEGUMENT PROTEINS OF HERPES-SIMPLEX VIRUS-1

In cells infected with herpes simplex virus 1 (HSV-1), the viral prote ins ICPS (infected-cell protein 5) and VP19c (the product of U(L)38) a re associated with mature capsids, whereas the same proteins, along wi th ICP35, are components of immature capsids, Here we report that ICP3 5, ICP5, and U(L)38 (VP19c) coalesce at late times postinfection and f orm antigenically dense structures located at the periphery of nuclei, close to but not abutting nuclear membranes. These structures were fo rmed in cells infected with a virus carrying a temperature-sensitive m utation in the U(L)15 gene at nonpermissive temperatures, Since at the se temperatures viral DNA is made but not packaged, these structures m ust contain the proteins for immature-capsid assembly and were therefo re designated assemblons. These assemblons are located at the peripher y of a diffuse structure composed of proteins involved in DNA synthesi s. This structure overlaps only minimally with the assemblons. In cont rast, tegument proteins were located in asymmetrically distributed str uctures also partially overlapping with assemblons but frequently loca ted nearer to nuclear membranes, Of particular interest is the finding that the U(L)15 protein colocalized with the proteins associated with viral DNA synthesis rather than with assemblons, suggesting that the association with DNA may take plate during its synthesis and precedes the involvement of this protein in packaging of the viral DNA into cap sids. The formation of three different compartments consisting of prot eins involved in viral DNA synthesis, the capsid proteins, and tegumen t proteins suggests that there exists a viral machinery which enables aggregation and coalescence of specific viral protein groups on the ba sis of their function.