Nuclear magnetic resonance and nuclear Overhauser effect study of yeast phenylalanine transfer ribonucleic acid imino protons.

Results directed primarily toward spectral assignment and nuclear spin dynamics are described for yeast tRNAPhe in 0.1 M NaCl, pH 7. Magnesium titrations were performed. Changes in the spectrum occur for Mg2+/tRNA ratios of about 2 and above 10. Difference spectroscopy between 43 and 29 degrees C in zero Mg2+ concentration, together with prior identification of the GU4 acceptor stem base pair, indicates early acceptor melting and is used to identify acceptor resonances. Transport of spin energy (spin diffusion) is described in tRNA together with a summary of relevant experiments. A survey of nuclear Overhauser effects (NOE's) between imino and aromatic and amino protons is included, together with some recent conclusions based on methyl NOE's and experiments with tRNAs deuterated at the purine C8 position. Assignment of the imino NMR spectrum on the basis of these and previous data is reviewed and discussed in detail. Preliminary distance estimates based on the NOE for AU and GU4 base pairs are in reasonable agreement with the expected distances.