E-rns is an envelope glycoprotein of classical swine fever virus (CSFV) with unusual RNase activity. Recently, E-rns was found to have a new function of counteracting the beta-interferon (IFN-beta) induction pathway. In this study, wildtype E-sm(rns) and two mutated E-rns proteins E-rns (H297k) and E-rns (H346k) were expressed in insect cells and purified for RNase activity and function analysis. RNase activity assay in vitro demonstrated that only wildtype E-rns protein had RNase activity. However, both wildtype E-sm(rns) and the two mutated E-rns E-rns (H297k) and E-rns (H346k) as exogenous proteins had a block effect on Newcastle disease virus (NDV)-mediated IFN-beta promoter induction. (C) 2007 Elsevier Inc. All rights reserved.