Serine/Threonine kinase dependent transcription from the polyhedrin promoter of SpltNPV-I

Polyhedrin (polh) and p10 are the two hyper-expressed very late genes of nucleopolyhedroviruses. Alpha amanitin resistant transcription from Spodoptera litura nucleopolyhedrovirus (SpltNPV-I) polyhedrin promoter was observed with virus infected nuclear extract of NIV-HA-197 cells but not with that from uninfected nuclear extract. Anti-protein kinase-1 (pk1) antibody inhibited the transcription and the inhibition reversed on addition of pk1, however, pk1 mutant protein, K50M having no phosphorylation activity did not overcome the transcription inhibition. Chromatin immuno-precipitation assays with viral anti-pk1 antibody showed the interaction of pk1 with the polh while electrophoretic mobility shift assays indicated the strong binding affinity (Kd ∼ 5.5 × 10−11) of purified pk1 with the polh promoter. These results suggested that the viral coded pk1 acts as a transcription factor in transcribing baculovirus very late genes.