Method for splicing a target nucleic acid molecule with a separate nucleic acid molecule. Such splicing generally causes production of a chimeric protein with advantageous features over that protein naturally produced from the target nucleic acid prior to splicing. The method includes contacting the target nucleic acid molecule with a catalytic nucleic acid molecule including the separate nucleic acid molecule. Such contacting is performed under conditions in which at least a portion of the separate nucleic acid molecule is spliced with at least a portion of the target nucleic acid molecule to form a chimeric nucleic acid molecule. In this method, the catalytic nucleic molecule is chosen so that it is not naturally associated with the separate nucleic acid molecule.