Competition between baculovirus polyhedrin and p10 gene expression during infection of insect cells

Polyhedrin and p10 genes are expressed concurrently during the late stage of infection. To determine whether any competition occurs between these two genes at a transcriptional and/or translational level, a series of Autographa californica nuclear polyhedrosis recombinant viruses with deletions of promoter and coding sequences of the p10 or polyhedrin gene was constructed. Two modified baculoviruses with only one of the very late promoters, single late-promoter viruses AcSLP10 and AcSLP33, were made. The polyhedrin gene was used as a reporter gene to allow direct comparison between p10 and polyhedrin-driven expression. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis analysis and [35S]methionine labeling experiments showed that polyhedrin synthesis is enhanced in cells infected with baculoviruses carrying only one very late promoter. However, this enhancement is more significant when the polyhedrin gene is located in its natural site. Dot blot hybridization experiments carried out with total cytoplasmic RNA showed that deletion of the p10 promoter resulted in an increase of mRNAs derived from the polyhedrin promoter. In contrast, no increase of p10-promoted mRNA was detected when the polyhedrin gene promoter was deleted.