Summary auto-generated
Researchers isolated two morphology mutants (m-5 and m-6) of Autographa californica nuclear polyhedrosis virus (NPV) from cultures treated with the mutagen N-methyl-N'-nitro-N-nitrosoguanidine. Unlike wild-type virus, these mutants produced single, large cuboidal inclusion bodies instead of typical polyhedral shapes in infected insect cells. Electron microscopy revealed that the mutant inclusion bodies possessed normal crystalline lattice structures and envelopes similar to wild-type polyhedra, but rarely contained occluded viruses inside. When purified mutant inclusion bodies were fed to Trichoplusia ni larvae, they showed significantly lower infectivity compared to wild-type polyhedra. Biochemical analysis using SDS-PAGE revealed that m-5 polyhedrin migrated differently than wild-type and m-6 polyhedrin. Peptide mapping following protease digestion showed m-5 polyhedrin had an altered pattern distinct from wild-type and m-6. However, m-6 polyhedrin was biochemically indistinguishable from wild-type by these methods. The researchers concluded that the altered morphology could result from changes in polyhedrin composition undetectable by their methods, or from mutations affecting unidentified proteins.
Key findings
- Two morphology mutants (m-5 and m-6) of Autographa californica NPV form large cuboidal inclusion bodies instead of typical polyhedral shapes
- Mutant inclusion bodies rarely contain occluded viruses and show substantially lower infectivity to insect larvae compared to wild-type virus
- m-5 polyhedrin exhibits altered electrophoretic mobility and different peptide maps following protease digestion, while m-6 polyhedrin appears identical to wild-type by these analyses
- Both mutant inclusion bodies possess normal crystalline lattice structures and envelopes indistinguishable from wild-type polyhedra despite their altered morphology
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Abstract
Two morphology mutants designated m-5 and m-6, of Autographa californica nuclear polyhedrosis virus (NPV) were isolated from virus grown in the presence of N-methyl-N'-nitro-N-nitrosoguanidine. Infected cells contained single, large cuboidal inclusion bodies with a crystalline lattice ultrastructure and envelope similar to that of wild-type (wt) polyhedra. The inclusion bodies had low infectivity when fed to Trichoplusia ni larvae. The paracrystalline lattice structure of the mutants was similar to wt, but occluded viruses were rarely found within the mutants. The m-5 polyhedrin (mol. wt. 30000) could be distinguished from wt and m-6 polyhedrin on the basis of migration in SDS-PAGE gels. Peptide maps of polyhedrin were obtained following digestion with chymotrypsinogen or Staphylococcus aureus V8 protease. They were identical for m-6 and wt polyhedrin but m-5 polyhedrin gave a different pattern. Thus, the altered morphology may be due to a change in polyhedrin composition not detectable in m-6 polyhedrin by the methods used here, or it may be the result of a mutation affecting a protein not yet identified.
* Present Address: Département de Microbiologie, Centre Hospitalier Universitaire, Université de Sherbrooke, Sherbrooke, Québec, Canada J1H 5N4.