Identification of the US3 gene product of BHV-1 as a protein kinase and characterization of BHV-1 mutants of the US3 gene.

We have identified the product of the US3 gene of bovine herpes virus type 1 (BHV-1), which is homologous to the herpes simplex virus type 1 (HSV-1) US3 protein kinase (PK) gene. The antibodies against the BHV-1 US3 gene product reacted with a 58 kDa polypeptide in BHV-1 infected cells and the 58 kDa polypeptide purified by immuno-precipitation demonstrated PK activity. Recent reports indicating that the US3 gene of HSV-1 is involved in the blockage of apoptosis in virus infected cells. As to the apoptosis in BHV-1 infected cells, we found following: (1) no apoptosis was observed in cells infected with wild type BHV-1 and the US3 mutants (2) the apoptosis induced by the osmotic shock of sorbitol treatment was blocked when cells were infected by the wild type BHV-1 (3) the US3 mutants of BHV-1 blocked the apoptosis of sorbitol treated cell, but the suppressive effect was delayed relative to that of wild type BHV-1 (4) the other BHV-1 mutants, with the intact US3 gene but with some other non-essential gene (genes) deleted behaved similar way to the US3 mutant. It is concluded that the US3 gene of BHV-1 is not directly involved in the blockage of apoptosis in infected cells.