ORGYIA-PSEUDOTSUGATA BACULOVIRUS P10 AND POLYHEDRON ENVELOPE PROTEIN GENES - ANALYSIS OF THEIR RELATIVE EXPRESSION LEVELS AND ROLE IN POLYHEDRON STRUCTURE

To investigate the regulation of p10 and polyhedron envelope protein ( PEP) gene expression and their role in polyhedron development, Orgyia pseudotsugata multi-nucleocapsid nuclear polyhedrosis viruses lacking these genes were constructed. Recombinant viruses were produced, in wh ich the p10 gene, the PEP gene or both genes were disrupted with the b eta-glucuronidase (GUS) or beta-galactosidase (lacZ) genes. GUS activi ty under the control of the PEP protein promoter was observed later in infection and its maximal expression was less than 10% the level for p10 promoter-GUS constructs. Tissues from 0. pseudotsugata larvae infe cted with these recombinants were examined by electron microscopy. Cel ls from insects infected with the p10(-) viruses lacked p10-associated fibrillar structures, but fragments of polyhedron envelope-like struc tures were observed on the surface of some polyhedra. Immunogold label ling of cells infected with the p10(-)GUS(+) virus with an antibody di rected against PEP showed that the PEP was concentrated at the surface of polyhedra. Although polyhedra produced by p10 and PEP gene deletio n mutants demonstrated what appeared to be a polyhedron envelope by tr ansmission electron microscopy, scanning electron microscopy showed th at they had irregular, pitted surfaces that were different from wild-t ype polyhedra. These data suggested that both p10 and PEP are importan t for the proper formation of the periphery of polyhedra.