Figure 1.

(A) Schematic diagram of fragment 465N of E. coli alanyl-tRNA synthetase and the fusions to nonspecific RNA binding domains C^Arc1p and Ad^ScQRS. The class-defining active site region extends to His249 whereas a fragment produced by extensive proteolysis terminates at Arg368. The nonspecific RNA binding domains are schematically shown as ellipsoids. Conserved class II motifs in the class defining domain are labeled as 1, 2, and 3. (B) Sequence and cloverleaf structure of E. coli tRNA^Ala and sequence and hairpin structure of microhelix^Ala. The G3:U70 base pair is indicated by a shaded box.