VP16 INTERACTS VIA ITS ACTIVATION DOMAIN WITH VP22, A TEGUMENT PROTEIN OF HERPES-SIMPLEX VIRUS, AND IS RELOCATED TO A NOVEL MACROMOLECULAR ASSEMBLY IN COEXPRESSING CELLS

In addition to its function as a powerful transactivator of viral imme diate-early transcription, VP16 is an essential component of the herpe s simplex virus (HSV) virion. As such, VP16 is introduced into cells, to effect its function in transactivation, as part of the virus tegume nt. Here we examine the potential for VP16 protein-protein interaction s specific to virus-infected cells and show that VP16 copurifies in a highly enriched fraction with a single major polypeptide which we iden tify as the virus-encoded structural protein VP22. We further show tha t in vitro-translated VP22 binds specifically to purified VP16. The ac tivation domain of VP16 was required and largely sufficient for this b inding. Mutations within this domain, which disrupt its transactivatio n function, also affected VP22 binding. Furthermore, we show that whil e VP16 and VP22 showed distinct patterns of compartmentalization in vi vo, coexpression of both proteins resulted in a profound reorganizatio n from their normal locations to a novel macromolecular assembly. The colocalization was also dependent on the activation domain of VP16 but required additional determinants within the N terminus. These results are discussed in the context of VP16 regulation of transcription both early in infection during delivery of tegument proteins and at late t imes during virus assembly.