2-5A-dependent RNase Molecules Dimerize during Activation by 2-5A (*)

2-5A-dependent RNase is an interferon-inducible enzyme that requires 5′-phosphorylated, 2′,5′-linked oligoadenylates (2-5A) for its endoribonuclease activity against single-stranded RNAs. We demonstrate here that recombinant, human 2-5A-dependent RNase forms stable homodimers during its stimulation by 2-5A. The protein dimers were observed to form only upon binding to 2-5A, as shown using gel filtration chromatography and chemical cross-linking and after centrifugation in glycerol gradients. A monoclonal antibody to 2-5A-dependent RNase was prepared and used to probe the subunit structure of the enzyme in the presence or absence of 2-5A. Using oligoadenylates of different length, structure, and 5′-phosphorylation states we determined that conversion of 2-5A-dependent RNase from its monomeric, inactive form to its homodimeric, active form required the presence of functional 2-5A. These results demonstrate that the catalytically active form of 2-5A-dependent RNase is a homodimer.