EXPRESSION OF NONSTRUCTURAL PROTEIN NS3 OF AFRICAN HORSESICKNESS VIRUS (AHSV) - EVIDENCE FOR A CYTOTOXIC EFFECT OF NS3 IN INSECT CELLS, ANDCHARACTERIZATION OF THE GENE-PRODUCTS IN AHSV INFECTED VERO CELLS

The smallest genome segment of African horsesickness virus (AHSV), seg ment 10 (S10), encodes two minor nonstructural proteins, NS3 and NS3A. While the cognate bluetongue virus (BTV) proteins have been suggested to play a role in the release of virus particles from infected cells, no function has yet been ascribed to AHSV NS3/NS3A. When the AHSV-3 S 10 gene was expressed in a baculovirus system only a single NS3 protei n (24 K) was synthesized, at lower levels than expected. It was shown that this could be due to a membrane association of NS3, leading to an alteration in host cell membrane permeability and eventual cell death . Based on computer predictions a general model for the membrane-assoc iated topology of NS3 of five different orbiviruses was proposed. Stud ies on AHSV-3 infected Vero cells showed that equimolar amounts of NS3 and NS3A were synthesized. No evidence was found for the glycosylatio n of NS3. The S10 genes and NS3/3A proteins of AHSV-3 and AHSV-7 were shown to be closely related, and clearly distinct from the cognate pro teins of the other 7 AHSV serotypes. This distinguishes the AHSV S10 g ene product from that of BTV NS3, which appears to be much more conser ved.