Basis for regulated RNA cleavage by functional analysis of RNase L and Ire1p

RNase L and Ire1p are members of a superfamily of regulated endoribonucleas es that play essential roles in mediating diverse types of cellular stress responses. 2 ' -5 ' oligoadenylates, produced in response to interferon tre atment and viral double-stranded RNA, are necessary to activate RNase L, In contrast, unfolded proteins in the endoplasmic reticulum activate Ire1p, a transmembrane serine/threonine kinase and endoribonuclease, To probe their similarities and differences, molecular properties of wild-type and mutant forms of human RNase L and yeast Ire1p were compared. Surprisingly, RNase L and Ire1p showed mutually exclusive RNA substrate specificity and partial ly overlapping but not identical requirements for phylogenetically conserve d amino acid residues in their nuclease domains. A functional model for RNa se L was generated based on the comparative analysis with Ire1p that assign s novel roles for ankyrin repeats and kinase-like domains.