NMR investigation of proton exchange in transfer rna by high resolution NMR

High resolution (300 MHz) nmr has been used to follow the exchange-out of ring NH protons involved in watson-Crick secondary structure base pairs in yeast tRNA 3 Leu and tRNA Phe. At 4°C the ∼20 resonances observed in the low field region of the spectrum (11 to 15 ppm) exchange with the solvent (D 2O) in less than 300 sec. Because the exchange—out is so rapid, we are unable to follow the behavior of imino protons in specific watson-Crick base pairs. The 20–40 very slowly (1 hr.) exchanging protons observed by tritium exchange must be assigned to amino protons.