Characterization of ORF2 and its encoded protein of the Helicoverpa armigera nucleopolyhedrovirus

The open reading frame 2 (ha2) of the Helicoverpa armigera single nucleocapsid nucleopolyhedrovirus (HaSNPV), a conserved gene in most baculoviruses from lepidopteran insects such as p78/83 of the Autographa californica MNPV, was characterized. It is 1242 bp long and potentially encodes a 45.9 kDa. Ha2 is conserved among baculoviruses from lepidopteran insects. Ha2 transcripts were detected from 16 to 96 h post infection (hpi) of HzAM1 cells. Rabbit polyclonal antiserum against a GST-HA2 fusion protein reacted with three protein of 50, 46 and 35 kDa at 24–72 hpi of HzAM1 cells. Anti OpMNPV ORF2 (homologue of HA2) antibody reacted only with the 46 and 35 kDa proteins in HaSNPV-infected cells. These results demonstrate that Ha2 is modified at the mRNA or protein levels. Western blot analysis showed that only the 50 kDa product of HA2 is a structural component of proteins of both the budded virus (BV) and occlusion-derived virus (ODV) phenotypes. HA2-EGFP fusion protein showed that HA2 is localized primarily in the nucleus of HzAM1 infected cells. The HA2 was found to co-localize with actin by labelling of actin with Rhordamine-Phalloidin. In summary, the data indicated that HA2 is a structural protein and interacts with host cell actin.