THE MULTIMERIC NONSTRUCTURAL NS2 PROTEINS OF BLUETONGUE VIRUS, AFRICAN HORSESICKNESS VIRUS, AND EPIZOOTIC HEMORRHAGIC-DISEASE VIRUS DIFFER IN THEIR SINGLE-STRANDED RNA-BINDING ABILITY

The structure and single-stranded (ss) RNA-binding by the nonstructura l protein NS2 of three different orbiviruses were studied and compared . African horsesickness virus (AHSV), bluetongue virus (BTV), and epiz ootic hemorrhagic disease virus (EHDV) were analyzed in recombinant ba culovirus-infected cells and in cells infected with BTV and AHSV. Sedi mentation analysis and nonreducing SDS-PAGE revealed that NS2 of all t hree orbiviruses is a 7S multimer with both inter- and intramolecular disulfide bonds, probably consisting of six or more NS2 molecules. The 7S NS2 multimer of all three viruses binds ssRNA but there is a marke d disparity in the ssRNA-binding ability between the three proteins. A t physiological salt concentration, BN NS2 binds ssRNA very efficientl y, whereas AHSV NS2 shows only a low efficiency for binding ssRNA. EHD V NS2 binds with intermediate efficiency. The result was the same irre spective of whether poly(U)-Sepharose or viral mRNA was used, indicati ng that ssRNA-binding by NS2 is nonspecific. The difference in RNA-bin ding ability may be related to the alpha-helix content of the respecti ve proteins. NS2 of BTV has the highest predicted alpha-helix content followed by EHDV and AHSV. The ability of the NS2 proteins to form vir us inclusion body-like structures in baculovirus-infected cells is not affected by the ssRNA-binding disparity. (C) 1995 Academic Press, Inc .