Cooperation of ie1 and p35 genes in the activation of baculovirus AcMNPV and HzNV-1 promoters

HzNV-1 is a non-occluded virus belongs to the family of the baculovirus. One of the first detectable transcripts expressed by HzNV-1 virus infection is a 6.2 kb gene, hhi1, located in the HindIII-I fragment of the viral genome. Here we show that infection of baculovirus Autographa californica multiple nucleopolyhedrovirus (AcMNPV) could activate the expression of the hhi1 promoter. By using constructs containing progressive deletions of the upstream regulatory regions of the hhi1 gene, we demonstrated that the most highly activated area was located between nucleotides −62 to +277 of the hhi1 promoter. We subsequently searched the entire 130 kb AcMNPV genome and identified two baculovirus genes, ie1 and p35, that their cooperation is required for the activation of the hhi1 promoter. Further, by taking advantages of a baculovirus DNA chip and low background baculovirus gene expressions in the mammalian cells, we went on to identify a specific set of baculoviral genes, including orf21 and orf25, that could be specifically activated by the combination of ie1 and p35 genes. We conclude that a unique cooperative mechanism of ie1 and p35 exists in the genome of AcMNPV, which can activate the expression of a specific set of AcMNPV and HzNV-1 promoters.