MULTIPLE-QUANTUM COHERENCE DRAMATICALLY ENHANCES THE SENSITIVITY OF CH AND CH2 CORRELATIONS IN UNIFORMLY C-13-LABELED RNA

One-bond H-1, C-13 and geminal H-1,H-1 dipolar interactions are normal ly the dominant causes of H-1 and C-13 transverse relaxation in NMR ex periments applied to C-13,N-15-labeled RNA in solution. Proton,carbon multiple-quantum coherences, where all heteronuclei connected by singl e bonds are evolved simultaneously in the transverse plane, however, a re not affected by these strong dipolar interactions. Consequently, th e transverse lifetimes, or T-2 values, of these resonances can be dram atically extended. Here, we show that pulse sequences can be written t hat take advantage of this effect to enhance the sensitivity with whic h CH and CH2 correlations are observed in uniformly C-13,N-15-labeled RNA oligonucleotides. In heteronuclear multiple-quantum correlation ex periments, CH and CH2 correlations are detected with a sensitivity tha t is enhanced by about a factor of 3 relative to heteronuclear, single -quantum experiments for a C-13,N-15-labeled 36mer RNA oligonucleotide and a constant time period of 25 ms. By including H-1, C-13 multiple- quantum coherence steps in an H-1, C-13, N-15 NMR experiment of the '' out and back'' type currently used for through-bond resonance assignme nt in RNA, we have obtained a sensitivity enhancement of about a facto r of 5 in the same 36mer RNA.