Structural Requirements at the 15.1–16.1 Position of the Hammerhead Ribozyme

Abstract Apart from the A15.1•U16.1 -> I15.1•C16.1 change which reverses the polarity of an important H-bond in the hammerhead structure no other functional group changes at the 15.1 purine residue seem to be compatible with the requirements of efficient catalysis. The I15.1 and A15.1 ribozymes are equally suitable for practical applications because there are only minor differences in the acceptance of stabilising residues.