THE SIR SUPPLIED DR. THEIL WITH 95MG [U-15N]GMP. THE IRE CIS ELEMENT IN EUKARYOTIC MRNA IS HIGHLY CONSERVED AND HAS A CHARACTERIZED SPECIFIC REGULATOR PROTEIN. OUR STUDIES OF FUNCTION AND STRUCTURE, USING SITE-DIRECTED MUTAGENESIS AND CLEAVAGE BY SHAPE-SELECTIVE TRANSITION METAL COMPLEXES AS STRUCTURE PROBES, INDICATE A FOLDED STRUCTURE WITH POSSIBLY UNUSUAL TERTIARY FEATURES. OUR PRELIMINARY NMR SPECTROSCOPY SHOWS THAT THE IRE SEQUENCE (A 30 MER) FORMS A SINGLE CONFORMER IN SOLUTION WHICH FACILITATES THE STRUCTURE ANALYSIS. THE USE OF 13C- AND 15N-ENRICHED RIBONUCLEOTIDES, UNIFORMLY LABELLED OR OTHERWISE, ARE CRUCIAL TO THE NMR STUDY.