1H NMR studies on the conformational characteristics of 2-thiopyrimidine nucleotides found in transfer RNAs

Abstract

The molecular conformations of naturally occurring 2-thiopyrimidine nucleosides (5-methylaminomethyl-2-thiouridine, 5-methoxycarbonylmethyl-2-thiouridine and 2-thiocytidine) and 5'-mononucleotides (5-methylaminomethyl-2-thiouridine 5'-monophosphate and 2-thiocytidine 5'-monophosphate) in 2H2O solution were elucidated by analyses of the proton NMR spin-coupling constant, nuclear Overhauser effect, and lanthanide-induced shifts and relaxation enhancements. As monomers, these nucleotides are almost exclusively in the 3E-gg-anti form, even in the absence of ordinary stabilizing factors of this form; i. e., base-stacking and base-pairing interactions with other nucleotide units. This inherent conformational rigidity of the 2-thiopyrimidine units probably contributes to stability of the conformation of tRNA.