CORRELATION OF THE GUANOSINE EXCHANGEABLE AND NONEXCHANGEABLE BASE PROTONS IN C-13-(IN)-N-15-LABELED RNA WITH AN HNC-TOCSY-CH EXPERIMENT

A triple resonance HNC-TOCSY-CH experiment is described for correlatin g the guanosine imino proton and H8 resonances in C-13-/N-15-labeled R NAs. Sequential assignment of the exchangeable imino protons in Watson -Crick base pairs is generally made independently of the assignment of the nonexchangeable base protons. This H(NC)-TOCSY-(C)H experiment ma kes it possible to unambiguously link the assign ment of the guanosine H8 resonances with sequential assignment of the guanosine imino proto n resonances. 2D H(NC)-TOCSY-(C)H spectra are presented for two isotop ically labeled RNAs, a 30-nucleotide lead-dependent ribozyme known as the leadzyme, and a 48-nucleotide hammerhead ribozyme-RNA substrate co mplex. The results obtained on these two RNAs demonstrate that this HN C-TOCSY-CH experiment is an important tool for resonance assignment of isotopically labeled RNAs.