The herpes simplex virus type 1 U(S)11 protein interacts with protein kinase R in infected cells and requires a 30-amino-acid sequence adjacent to a kinase substrate domain

The herpes simplex virus type 1 gamma(1)34.5 gene product precludes the host-mediated protein shutoff response induced by activated protein kinase R (PKR). Earlier studies demonstrated that recombinant viruses lacking the gamma(1)34.5 gene (Deltagamma(1)34.5) developed secondary mutations that allowed earlier U(S)11 expression and enabled continued protein synthesis. Further, in vitro studies demonstrated that a recombinant expressed U(S)11 protein binds PKR, blocks the phosphorylation of the alpha subunit of eukaryotic initiation factor 2 (eIF-2alpha) by activated PKR, and, if provided prior to PKR activation, precluded PKR autophosphorylation. The present study furthers the hypothesis that early U(S)11 production precludes PKR-mediated host protein shutoff by demonstrating that (i) U(S)11 and PKR interact in the context of viral infection, (ii) this interaction is RNA dependent and requires a 30-amino-acid domain (amino acids 91 to 121) in the carboxyl domain of the U(S)11 protein, (iii) the proteins biochemically colocalize in the S100 ribosomal fraction, and (iv) there is a PKR substrate domain immediately adjacent to the binding domain. The results suggest that the U(S)11 interaction with PKR at the ribosome is RNA dependent and that the U(S)11 protein contains a substrate domain with homology to eIF-2alpha in close proximity to an essential binding domain.