CLONING AND CHARACTERIZATION OF A RNASE-L INHIBITOR - A NEW COMPONENTOF THE INTERFERON-REGULATED 2-5A PATHWAY

The 2-5A/RNase L system is considered as a central pathway of interfer on (IFN) action and could possibly play a more general physiological r ole as for instance in the regulation of RNA stability in mammalian ce lls. We describe here the expression cloning and initial characterizat ion of RLI (for RNase L inhibitor), a new type of endoribonuclease inh ibitor. RLI cDNA codes for a 68-kDa polypeptide whose expression is no t regulated by IFN. Its expression in reticulocyte extracts antagonize s the 2-5A binding ability and the nuclease activity of endogenous RNa se L or the cloned 2DR polypeptide. The inhibition requires the associ ation of RLI with the nuclease and is dependent on the ratio between t he two proteins. Likewise RLI is coimmunoprecipitated with the RNase L complex by a nuclease specific antibody. RLI does not lead to 2-5A de gradation or to irreversible modification of RNase L. The overexpressi on of RLI in stably transfected HeLa cells inhibits the antiviral acti vity of IFN on encephalomyocarditis virus but not on vesicular stomati tis virus.RLI therefore appears as the first described and potentially important mediator of the 2-5A/RNase L pathway.