Interaction between herpes simplex virus type 1 IE63 protein and cellular protein p32

The herpes simplex virus type 1 (HSV-1) immediate-early gene IE63 (ICP27), the only HSV-1 regulatory gene with a homologue in every mammalian and avia n herpesvirus sequenced so far, is a multifunctional protein which regulate s transcriptional and posttranscriptional processes. One of its posttranscr iptional effects is the inhibition of splicing of viral and cellular transc ripts. We previously identified heterogeneous nuclear ribonucleoprotein (hn RNP) K and casein kinase 2 (CK2) as two protein partners of IE63 (H. Bryant et al., J. Biol. Chem. 274:28991-28998, 1999). Here, using a yeast two-hyb rid assay, we identify another partner of IE63, the cellular protein p32. C onfirmation of this interaction was provided by coimmunoprecipitation from virus-infected cells and recombinant p32 binding assays. A p32-hnRNP K-CK2 complex, which required IE63 to form, was isolated from HSV-1-infected cell s, and coimmunoprecipitating p32 was phosphorylated by CK2. Expression of I E63 altered the cytoplasmic distribution of p32, with some now colocalizing with IE63 in the nuclei of infected and transfected cells. As p32 copurifi es with splicing factors and can inhibit splicing, we propose that IE63 tog ether with p32, possibly with other IE63 partner proteins, acts to disrupt or regulate pre-mRNA splicing. As well as contributing to host cell shutoff , this effect could facilitate splicing-independent nuclear export of viral transcripts.