Fig. 3. Structure-based sequence alignment of the proposed αL RNA-binding motif in heat shock protein 15 kDa (Hsp15), ribosomal protein S4 (S4) and threonyl-tRNA synthetase (Thr-RS). Only the portion of each protein sequence that is structurally similar is shown. The secondary structures as identified by RIBBONS (Carson, 1997) are shown above the sequence alignments. Residues that are >50% conserved or identical within each family are shown in bold upper case letters. Residues in bold green upper case letters are both conserved in at least 50% of the members of each family, and are solvent accessible as determined by XPLOR (Brünger, 1997). Residues that are similar between at least two of the three structures are shaded gray.