Characterization of a late gene, ORF75 from Bombyx mori nucleopolyhedrovirus

Area of Science:

• Virology
• Molecular Biology
• Insect Pathology

Background:

• The Bombyx mori nucleopolyhedrovirus (BmNPV) Bm-p33 gene is a homologue of Autographa californica multiple nucleopolyhedrovirus ORF92.
• Bm-p33 is conserved across sequenced baculoviruses and considered a core set gene.
• No amino acid mutations were found in Bm-p33 across different BmNPV strains.

Purpose of the Study:

• To characterize the expression pattern and cellular localization of the Bm-p33 protein in BmNPV-infected cells.
• To investigate the function of Bm-p33 in the viral life cycle, particularly in virion formation.

Main Methods:

• Quantitative analysis of Bm-p33 mRNA and protein expression over time post-infection.
• Western blot analysis to detect Bm-p33 in different virus forms (BVs and ODVs).
• Immunofluorescence microscopy for cellular localization studies.
• RNA interference (RNAi) to assess the impact of Bm-p33 depletion on viral production.

Main Results:

• Bm-p33 transcript detected from 12 to 96 hours post-infection (h p.i.), with protein detectable from 18 to 96 h p.i.
• Bm-p33 protein was not found in budded viruses (BVs) or occlusion-derived viruses (ODVs).
• Immunofluorescence showed Bm-p33 accumulation in the nuclear membrane and intranuclear regions.
• Bm75 RNAi reduced Bm-p33 mRNA levels, but no significant effects on ODV formation or BV production were observed.

Conclusions:

• Bm-p33 is a BmNPV late gene encoding a nonstructural protein.
• The protein primarily functions within the nucleus of infected cells.
• Despite nuclear localization, Bm-p33 does not appear essential for ODV or BV production in BmNPV-infected cells.