Characterization of tubular structures composed of nonstructural protein NS1 of African horsesickness virus expressed in insect cells.

The characteristic tubules that are produced during the orbivirus infection cycle are composed of a major viral nonstructural protein, NS1. To characterize the NS1 gene and gene product of African horsesickness virus (AHSV), a full-length cDNA copy of the NS1 gene of AHSV-6 was cloned and the nucleotide sequence determined. NS1 was highly conserved within the AHSV serogroup with between 95-98% conservation of amino acids among NS1 of AHSV-6, AHSV-4 and AHSV-9. The structure of AHSV NS1 tubules was investigated by in vitro translation of the AHSV-6 NS1 gene followed by expression of the gene in insect cells. The NS1 protein assembled in tubular structures with a diameter of approximately 23 nm and lengths of up to 4 microns. The absence of a ladder-like structure and lower sedimentation value of AHSV NS1 tubules clearly distinguished them from those of bluetongue virus.