THE IMPORTANCE OF TRANSFER-RNA BACKBONE-MEDIATED INTERACTIONS WITH SYNTHETASE FOR AMINOACYLATION

We have identified six new aminoacylation determinants of Escherichia coli tRNA(Gln) in a genetic and biochemical analysis of suppressor tRN A, The new determinants occupy the interior of the acceptor stem, the inside corner of the L shape, and the anticodon loop of the molecule, They supplement the primary determinants located in the anticodon and acceptor end of tRNA(Gln) described previously. Remarkably, the three- dimensional structure of the complex between tRNA(Gln) and glutaminyl- tRNA synthetase shows that the enzyme interacts with the phosphate-sug ar backbone but not the base of every nem determinant, Moreover, a sma ll protein motif interacts with five of these determinants, and it bin ds proximal to the sixth, The motif also interacts with the middle bas e of the anticodon and with the backbones of six other nucleotides. Ou r results emphasize that synthetase recognition of tRNA is more elabor ate than amino acid side chains of the enzyme interacting with nucleot ide bases of the tRNA. Recognition also includes synthetase interactio n with tRNA backbone functionalities whose distinctive locations in th ree-dimensional space are exquisitely determined by the tRNA sequence.