RNA binding properties of the US11 protein from four primate simplexviruses

BACKGROUND: The protein encoded by the Us11 gene of herpes simplex viruses is a dsRNA binding protein which inhibits protein kinase R activity, thereby preventing the interferon-induced shut down of protein synthesis following viral infection. Us11 protein is not essential for infectivity in vitro and in mice in herpes simplex virus type 1 (HSV1), however this virus has a second, and apparently more important, inhibitor of PKR activity, the γ(1)34.5 protein. Recently sequenced simian simplexviruses SA8, HVP2 and B virus do not have an ORF corresponding to the γ(1)34.5 protein, yet they have similar, or greater, infectivity as HSV1 and HSV2. METHODS: We have expressed the US11 proteins of the simplexviruses HSV1, HSV2, HVP2 and B virus and measured their abilities to bind dsRNA, in order to investigate possible differences that could complement the absence of the γ(1)34.5 protein. We employed a filter binding technique that allows binding of the Us11 protein under condition of excess dsRNA substrate and therefore a measurement of the true Kd value of Us11-dsRNA binding. RESULTS AND CONCLUSIONS: The results show a Kd of binding in the range of 0.89 nM to 1.82 nM, with no significant difference among the four Us11 proteins.