Abstract
IgG purified from sera of several patients with systemic lupus erythematosus and hepatitis B are shown to present RNA hydrolyzing activities that are different from the weak RNase A-type activities found in the sera of healthy donors. Further investigation brings evidence for two intrinsic activities, one observed in low salt conditions and another specifically stimulated by Mg2+ions and distinguishable from human sera RNases. Cleavage of RNA substrates by the latter activity is not sequence-specific but sensitive to both subtle conformational and/or drastic folding changes, as evidenced by comparative analysis of couples of structurally well-studied RNA substrates. These include yeast tRNAAsp and its in vitro transcript and human mitochondrial tRNALys-derived in vitro transcripts. The discovery of catalytic antibodies with RNase activities is a first step towards creation of a new generation of tools for the investigation of RNA structure.