A point mutation in the polyhedrin gene of a baculovirus, Autographa californica MNPV, prevents crystallization of occlusion bodies.

The polyhedrin gene region of the Autographa californica nuclear polyhedrosis virus(AcMNPV) morphology mutant M29 has been characterized by genetic and physical techniques. Recombination analysis of mutants M29 and AcM5polyl demonstrated that wild-type polyhedrin recombinants could be obtained and that the DNA restriction patterns of the recombinant viruses were identical to wild-type AcMNPV DNA. Marker rescue experiments using the wild-type AcMNPV EcoRI I fragment indicated that the morphology mutation responsible for the M29 phenotype was located in the 0.0 to 5.9 % region of the genome. Direct DNA sequencing of the BamHIF fragment from M29 showed a single point mutation at position 253 of the polyhedrin gene. This mutation caused a substitution of phenylalanine for leucine at amino acid 84 of the M29 polyhedrin protein. These results indicated the necessity of amino acid conservation in the polyhedrin amino acid sequence for proper folding and assembly of the polypeptide into occlusion bodies.