A COMMON PATHWAY FOR P10 AND CALYX PROTEINS IN PROGRESSIVE STAGES OF POLYHEDRON ENVELOPE ASSEMBLY IN ACMNPV-INFECTED SPODOPTERA-FRUGIPERDA LARVAE

The assembly of the polyhedron envelope in baculovirus-infected cells has been the subject of several studies, yet it is still poorly unders tood. We have used immunogold-labelled antibodies to two baculovirus p roteins, p10 and calyx (also referred to as polyhedron envelope protei n or PEP), to follow envelope assembly in AcMNPV-infected tissues of S podoptera fugiperda larvae. We show that, in wild type virus, both pro teins colocalize in fibrillar structures and associated electron-dense spacers which progress to encircle the polyhedra, as well as in compl eted polyhedron envelopes. In cells infected with polyhedrin-negative (PH-) viruses, an unusual proliferation of these spacers was observed suggesting a deregulatory event in the envelope assembly process. Resu lts of Northern and Western blot analysis revealed that synthesis of P 10 and calyx mRNA and proteins in PH- AcMNPV is unaffected as compared to wild type virus. Taken together, the observed physical and composi tional connection between fibrillar structures, spacers and polyhedron envelopes, as well as the abnormal appearance of the spacers in PH- m utants, provide further evidence in support of a cooperative role of t hese structures in the assembly of the polyhedron envelope.