NMR evidence for helix geometry modifications by a G-U wobble base pair in the acceptor arm of E. coli tRNAAla

Abstract
A ribooligonucleotide duplex representing the acceptor stem of E. coli RNA Ala with a G3‐U70 wobble base pair, which is the main identity element for the recognition by the alanine‐tRNA synthetase, has been characterized by 2D‐NMR, as having two sequence variants with a regular Watson‐Crick G3‐C70 and an I3‐U70 wobble pair, respectively. As compared to a regular A‐RNA, the G‐U base pair gives rise to variations of the local helix geometry which are reflected in distinct local chemical shift changes. Structural differences between the duplex possessing an 13‐U70 base pair and the wild‐type G3‐U70 sequence have also been found. The nucleotides in the ubiquitous single‐stranded NCCA terminus display a surprisingly high degree of stacking order, especially between A73, C74, and C75.