Aa. Szewczak et al., ASSIGNMENT OF NH RESONANCES IN NUCLEIC-ACIDS USING NATURAL-ABUNDANCE N-15-H-1 CORRELATION SPECTROSCOPY WITH SPIN-ECHO AND GRADIENT PULSES, FEBS letters, 327(3), 1993, pp. 261-264
It is well known that 2D N-15-H-1 correlation spectra can resolve over
lapped imino proton resonances in the downfield NMR spectra of nucleic
acids according to their N-15 chemical shifts, and that these resonan
ces can be assigned by base type on that basis, independent of conform
ation. This information can be extremely important in determining the
solution structure of a nucleic acid by NMR, but previously could only
be obtained using N-15-labeled, or very concentrated samples. Here we
report the design of a gradient-enhanced, jump-return spin echo versi
on of an N-15-H-1 HMQC experiment (GE-JRSE HMQC) that is sensitive eno
ugh to work on unlabeled nucleic acid samples at normal NMR concentrat
ions. This experiment has led to the assignment of imino proton resona
nces with non-Watson-Crick chemical shifts in the spectrum of a 29 res
idue oligoribonucleotide that models the sarcin/ricin loop from 28S rR
NA.