Biosynthesis and localization of the Autographa californica nuclear polyhedrosis virus 25K gene product.

Mutations of the AcMNPV 25K gene are associated with the "few polyhedra" phenotype (M. J. Fraser et al., 1983, J. Virol. 47, 287-300; B. Beames and M. D. Summers, 1989, Virology 168, 344-353). Polyclonal antisera was produced and used to investigate the time course of expression and localization of the 25K protein in infected cells. Western blot analysis detected 25K protein in both cytosolic and nuclear extracts from 18-24 hr p.i. through 96 hr p.i. and also in purified viral occlusions, but not in purified virions. Immunogold electron microscopy revealed that 25K protein was predominantly associated with amorphous cytoplasmic structures and to a lesser extent with a more electron-dense structure in the nucleus. Viral occlusions in cell sections were not specifically labeled by 25K antibody. Observations of purified viral occlusions and nuclei prepared for immunogold EM revealed the presence of contaminating amorphous material that was labeled with 25K antibody.