FUNCTIONAL-ANALYSIS OF PEPTIDE MOTIF FOR RNA MICROHELIX BINDING SUGGESTS NEW FAMILY OF RNA-BINDING DOMAINS

RNA microhelices that recreate the acceptor stems of transfer RNAs are charged,vith specific amino acids. Here we identify a two-helix pair in alanyl-tRNA synthetase that is required for RNA microhelix binding. A single point mutation at an absolutely conserved residue in this mo tif selectively disrupts RNA binding without perturbation of the catal ytic site. These results, and findings of similar motifs in the proxim ity of the active sites of other tRNA synthetases, suggest that two-he lix pairs are widespread and provide a structural framework important for contacts with bound RNA substrates.