ANALYSIS OF POLYHEDRA MORPHOLOGY MUTANTS OF AUTOGRAPHA-CALIFORNICA NUCLEAR POLYHEDROSIS-VIRUS - MOLECULAR AND ULTRASTRUCTURAL FEATURES

Two new mutants of Autographa californica multiple nuclear polyhedrosis virus affected in the morphogenesis of their polyhedra, designated M276 and M934, were investigated. Marker transfer experiments demonstrated that the observed phenotype was due exclusively to alterations in the polyhedrin gene. M276 contained a 229 base insertion near the carboxyl terminus coding region which resulted in synthesis of a truncated protein; M934 had a point mutation substituting phenylalanine for leucine at amino acid 183. Both mutations occurred in highly conserved regions of the protein and prevented the occlusion of virus particles, but did not affect targeting for the intra-nuclear ring zone. M276 was distinct in that it had prominent cytosolic condensations of polyhedrin, although these were probably due to decreased protein solubility. M934 polyhedrin condensations associated prematurely with calyx material such that it became incorporated into the condensation rather than at the surface. Results confirm that occlusion size and shape are features inherent to the polyhedrin protein, and suggest that polyhedrin conformation may help regulate the occlusion process.