EFFECTS OF SUBSTITUTING GRANULIN OR A GRANULIN-POLYHEDRIN CHIMERA FORPOLYHEDRIN ON VIRION OCCLUSION AND POLYHEDRAL MORPHOLOGY IN AUTOGRAPHA-CALIFORNICA MULTINUCLEOCAPSID NUCLEAR POLYHEDROSIS-VIRUS

Substitution of granulin from the Trichoplusia ni granulosis virus (Tn GV) for polyhedrin of the Autographa californica multinucleocapsid nuc lear polyhedrosis virus (AcMNPV) yielded a few very large (2 to 5 mu m ) cuboidal inclusions in the cytoplasm and nucleus of infected cells. These polyhedra lacked the beveled edges characteristic of wild-type A cMNPV polyhedra, contained fractures, and occluded few virions. Placin g a nuclear localization signal (KRKK) in granulin directed more granu lin to the nucleus and resulted in more structurally uniform cuboidal inclusions in which no virions were observed. A granulin-polyhedrin ch imera produced tetrahedral occlusions with more virions than granulin inclusions but many fewer than wild-type polyhedra, Despite the unusua l structure of the granulin and granulin-polyhedrin inclusions, they i nteracted with AcMNPV p10 fibrillar structures and electron-dense spac ers that are precursors of the polyhedral calyx. The change in inclusi on shape obtained with the granulin-polyhedrin chimera demonstrates th at the primary amino acid sequence affects occlusion body shape, but t he large cuboidal inclusions formed by granulin indicate that the amin o acid sequence is not the only determinant. The failure of granulin o r the granulin-polyhedrin chimera to properly occlude AcMNPV virions s uggests that specific interactions occur between polyhedrin and other viral proteins which facilitate normal virion occlusion and occlusion body assembly and shape in baculoviruses.