CHARACTERIZATION OF VIRAL ENHANCING ACTIVITY FROM TRICHOPLUSIA NI GRANULOSIS-VIRUS

A factor present in the granules of Trichoplusia ni granulosis virus, when fed together with a nuclear polyhedrosis virus, can enhance viral infection and accelerate death in T. ni neonate larvae. Occlusion bodies of T. ni granulosis virus were dissolved in alkali and soluble proteins were separated by gel filtration chromatography. These fractions were assayed for enhancement of nuclear polyhedrosis infection in T. ni neonates. Denaturing gel electrophoresis of the fractions revealed that enhancin, a protein homologous to the synergistic factor of Pseudaletia unipuncta, eluted as a discrete peak. Viral enhancing activity eluted over a large volume covering this peak and a wide molecular weight range following this peak. Moreover, we show that the 98-kDa enhancin protein is released from a larger 150-kDa complex, by heating in the presence of detergent. Once released, the enhancin protein is subject to extensive proteolysis, yielding smaller protein fragments. These results suggest the possibility that fragments of the enhancin protein, or other components of the 150-kDa complex, may be active viral enhancing agents. (C) 1995 Academic Press, Inc.