Enzymic and biophysical studies with purified IGV nucleic acid indicated that the virion contained a double-stranded RNA genome of .apprx. 14 .times. 106 daltons which could be separated by gel electrophoresis into 8 bands of RNA which were comprised of 15 RNA species. Two major virus proteins, VP2 (MW = 135,000) and VP8 (MW = 40,000), which composed .apprx. 85% of the total virion protein, were detected in IGV particles by polyacrylamide gel electrophoresis. Eight additional minor proteins were resolved.