MIRROR-IMAGE ALTERNATIVE INTERACTION PATTERNS OF THE SAME TRANSFER-RNA WITH EITHER CLASS-I ARGINYL-TRANSFER-RNA SYNTHETASE OR CLASS-II ASPARTYL-TRANSFER-RNA SYNTHETASE

Gene cloning, overproduction and an efficient purification protocol of yeast arginyl-tRNA synthetase (ArgRS) as well as the interaction patt erns of this protein with cognate tRNA(Arg) and non-cognate tRNA(Asp) are described, This work was motivated by the fact that the in vitro t ranscript of tRNA(Asp) is of dual aminoacylation specificity and is no t only aspartylated but also efficiently arginylated. The crystal stru cture of the complex between class II aspartyl-tRNA synthetase (AspRS) and tRNA(Asp), as well as early biochemical data, have shown that tRN A(Asp) is recognized by its variable region side, Here we show by foot printing with enzymatic and chemical probes that transcribed tRNA(Asp) is contacted by class I ArgRS along the opposite D arm side, as is ho mologous tRNA(Arg), but with idiosyncratic interaction patterns, Besid es protection, footprints also show enhanced accessibility of the tRNA s to the structural probes, indicative of conformational changes in th e complexed tRNAs, These different patterns are interpreted in relatio n to the alternative arginine identity sets found in the anticodon loo ps of tRNA(Arg) and tRNA(Asp), The mirror image alternative interactio n patterns of unmodified tRNA(Asp) with either class I ArgRS or class II AspRS, accounting for the dual identity of this tRNA, are discussed in relation to the class defining features of the synthetases, This s tudy indicates that complex formation between unmodified tRNA(Asp) and either ArgRS and AspRS is solely governed by the proteins.