Heliocoverpa armigera single nucleocapsid nucleopolyhedrovirus ORF52 is a ChaB homologous gene involved in per os infection

The baculovirus ChaB proteins are conserved in all completely sequenced Lepidopteran NPVs and are annotated as putative DNA binding proteins. In our previous study, ORF51, a ChaB homologue from Helicoverpa armigera single nucleocapsid nucleopolyhedrovirus (HearNPV) was found to be involved in budded virus production and DNA replication. In the present study, we characterized ORF52 (Ha52), the other ChaB homologous gene in HearNPV. 5′-RACE revealed that Ha52 was transcribed from a conventional late promoter transcriptional initiator motif (TAAG) located 25 nucleotides upstream of ATG. Expression analysis demonstrated that HA52 protein was expressed from 48 to 96 h post infection. Western blot analysis of virions from both budded viruses (BVs) and occlusion-derived viruses (ODVs) indicated that HA52 was a structural component of nucleocapsid from ODV. To study the function of Ha52 in the life cycle of HearNPV, Ha52-knockout and Ha52-restored viruses were generated by the Bac-to-Bac system. Growth curve analyses showed that the level of BV production in cells infected with Ha52 null virus was similar to those infected with wild-type bacmid derived virus. However, bioassay showed that deletion of Ha52 significantly decreased the per os infectivity of HearNPV. Taken together, our results indicated that, unlike the previously characterized baculovirual ChaB genes, Ha52 may be involved in HearNPV per os infection.