Role of the cytoplasmic tail of pseudorabies virus glycoprotein E in virion formation

Glycoproteins M (gM), E (gE), and I (gI) of pseudorabies virus (PrV) are re quired for efficient formation of mature virions. The simultaneous absence of gM and the gE/gI complex results in severe deficiencies in virion morpho genesis and cell-to cell spread, leading to drastically decreased virus tit ers and a small-plaque phenotype (A, Brack, J, Dijkstra, H, Granzow, B, G, Klupp, and T, C, Mettenleiter, J, Virol, 73:5364-5372, 1999), Serial passag ing in noncomplementing cells of a virus mutant unable to express gM, gE, a nd gI resulted in a reversion of the small-plaque phenotype and restoration of infectious virus formation to the level of a gM(-) mutant, Genetic anal yses showed that reversion of the phenotype was accompanied by a genomic re arrangement which led to the fusion of a portion of the gE gene encoding th e cytoplasmic domain to the 3' end of the glycoprotein D gene, resulting in expression of a chimeric gD-gE protein. Since this indicated that the intr acytoplasmic domain of gE was responsible for the observed phenotypic alter ations, the UL10 (gM) gene was deleted in a PrV mutant, PrV-107, which spec ifically lacked the cytoplasmic tail of gE, Regarding one-step growth, plaq ue size, and virion formation as observed under the electron microscope, th e mutant lacking gM and the gE cytoplasmic tail proved to be very similar t o the gE/I/M triple mutant. Thus, our data indicate that it is the cytoplas mic tail of gE which is responsible for the observed phenotypic effects in conjunction with deletion of gM. We hypothesize that the cytoplasmic domain of gE specifically interacts with components of the capsid and/or tegument , leading to efficient secondary envelopment of intracytoplasmic capsids.