ANALYSIS OF A VACCINIA VIRUS MUTANT EXPRESSING A NONPALMITYLATED FORMOF P37, A MEDIATOR OF VIRION ENVELOPMENT

Vaccinia virus encodes a 37-kDa palmitylated protein (p37) that is req uired for envelopment, translocation, and cell to-cell spread of,virio ns. We have analyzed the biological significance of the palmitate modi fication by constructing a recombinant vaccinia virus that expresses a nonpalmitylated p37 and comparing its biological activity to that of the wild-type virus. The mutant virus is inefficient at cell-to cell s pread and does not produce or release enveloped virions, although it p roduces normal amounts of nonenveloped virions. Furthermore, the mutan t virus is not able to nucleate actin to propel itself through and out of the cell, a function requiring the indirect participation of p37. The deficiency in protein function appears to result from a lack of ap propriate targeting to the membranes of the trans-Golgi network (TGN) which leaves p37 soluble in the cytoplasm. We conclude that the palmit ate moiety: is necessary for targeting or anchoring p37 to the TGN mem brane, where, along with other vaccinia virus-encoded proteins, p37 is involved in the complex process of virion envelopment and release.