The vaccinia virus 39-kDa protein forms a stable complex with the p4a/4a major core protein early in morphogenesis

The vaccinia virus (VV) 39-kDa protein, the product of the A4L gene, is a h ighly antigenic protein of the viral core. Pulse-chase and immunoprecipitat ion experiments have shown that the 39-kDa protein interacts with p4a (enco ded by the A10L gene), the precursor of the most abundant virion protein. T his interaction is maintained with the processed 4a form that arises during virion maturation. The controlled disruption of mature viral particles sho wed that the 39-kDa and 4a proteins are tightly bound within the virion. Im munoelectron microscopy showed that both proteins first localize within the cytoplasm and later accumulate inside the viral factories, reaching these locations via a mechanism apparently unrelated to cellular membranes. Doubl e labeling experiments showed a colocalization of both proteins in all viru s-induced structures. (C) 1999 Academic Press.