THE 85-KILODALTON PHOSPHOPROTEIN (PP85) OF HUMAN-HERPESVIRUS-7 IS ENCODED BY OPEN READING FRAME U14 AND LOCALIZES TO A TEGUMENT SUBSTRUCTURE IN VIRION PARTICLES

A family of antigenically related proteins present in cells infected w ith human herpesvirus 7 (HHV-7), designated phosphoprotein 85 (pp85), comprises a complex of proteins, of which the 85-kDa species is phosph orylated. pp85 is a major determinant of human response to HHV-7 infec tion (L. Foa-Tomasi, E. Avitabile, L. Ke, and G. Campadelli-Fiume, J. Gen. Virol. 75:2719-2727, 1994; L. Foa-Tomasi, M. P. Fiorilli, E. Avit abile, and G. Campadelli-Fiume, J. Gen. Virol. 77:511-518, 1996; J. B. Black et al., Clin. Diagn. Lab. Immunol. 3:79-83, 1996). By immunoscr eening of a cDNA library from HHV-7-infected cells with monoclonal ant ibody (MAb) 5E1, directed to the proteins of the pp85 complex, we mapp ed the gene encoding pp85 to the U14 open reading frame of the HHV-7 g enome. A prokaryotically expressed fusion protein containing the U14 o pen reading frame reacted with MAb 5E1 in an immunoblot assay. A funct ional role for pp85 was defined by immunoelectron microscopy studies. Immunogold labeling cryosections of HHV-7-infected cord blood mononucl ear cells at high resolution localized the reactivity of MAb 5E1 to th e outer surface of the virion tegument. This finding demonstrates that pp85, the product of the U14 gene, is a component of the HHV-7 tegume nt and suggests that the HHV-7 tegument is not a homogeneous structure but rather is composed of substructures, including an outermost layer containing pp85. The present findings, together with previously repor ted properties of MAb 5E1, including its ability to react with formali n-fixed paraffin-embedded samples, make this antibody a specific tool useful for etiopathogenetic studies of HHV-7 infection in human and pr ovide the basis for further development of pp85 into a specific recomb inant diagnostic reagent.