Qalyub virus, a member of the newly proposed Nairovirus genus (bunyavividae)

Abstract

Qalyub (QYB) virus, the prototype virus of the previously ungrouped QYB serogroup of arboviruses, has been shown by biochemical analyses of its structural polypeptides and virion RNA species to conform in broad terms to the criteria established for members of the Bunyaviridae family. QYB virus has a tripartite, single-stranded, RNA genome and three major structural proteins. The three viral RNA species each have unique sequences as shown by oligonucleotide fingerprint analyses and, from sedimentation and electrophoretic analyses, appear to have molecular weight values of 5 × 10 6 (L), 2 × 10 6 (M), and 0.7 × 10 6 (S). By comparison with the L RNA of other members of the Bunyaviridae family [see Bishop, D. H. L., and Shope, R. E., (1979). “Comprehensive Virology,” Vol. 14, pp. 1–156. Plenum, New York], QYB L RNA is apparently 50% larger. One of the QYB virion polypeptides is unglycosylated, 53 × 10 3 daltons in size, and associated with the viral RNA. It is consequently designated N. This N protein is approximately twice the size of the N proteins of the bunyavirus or other members of the family Bunyaviridae that have been studied (see Bishop and Shope, 1979). The other two QYB virion polypeptides are glycosylated (GI, 75 × 10 3; G2, 40 × 10 3) and can be removed from virions by protease treatment. Intracellular, glycosylated, large polypeptides (gp115, MW 115 × 10 3, and gp85, MW 85 × 10 3) are observed in QYB-infected cells, but not in purified virus preparations. From pulse-chase experiments, the large intracellular glycopolypeptides appear to be precursors of the virion glycopolypeptides. Recently, based on serologic studies, a new genus of viruses ( Nairovirus) in the family Bunyaviridae has been proposed. It includes the tick-borne Crimean-Congo hemorrhagic fever and Nairobi sheep disease serogroup viruses, together with the previously ungrouped Dera Ghazi Khan, QYB, and Hughes serogroup viruses [Casals, J., and Tignor, G. H. (1980). Intervirology, in press]. The biochemical data presented here on QYB virus support its inclusion in the family Bunyaviridae and indicate that, if borne out by studies of other members of these serogroups, the characteristics of the nairoviruses are different in many respects from those of viruses in other genera of the family Bunyaviridae.