Domain 5 is an essential active-site component of group II intron ribozymes. The role of backbone substituents in D5 function was explored through synthesis of a series of derivatives containing deoxynucleotides at each position along the D5 strand. Kinetic screens revealed that eight 2'-hydroxyl groups were likely to be critical for activity of D5. Through two separate methods, including competitive inhibition and direct kinetic analysis, effects on binding and chemistry were distinguished. Depending on their function, important 2'-hydroxyl groups lie on opposite faces of the molecule, defining distinct loci for molecular recognition and catalysis by D5.