Recognition of One tRNA by Two Classes of Aminoacyl-tRNA Synthetase

Abstract

Lysyl-tRNA synthetases are unique amongst the aminoacyl-tRNA synthetases in being composed of two unrelated families. In most bacteria and all eukarya, the known lysyl-tRNA synthetases are subclass He-type aminoacyl-tRNA synthetases whereas some archaea and bacteria have been shown to contain an unrelated class I-type lysyl-tRNA synthetase. We have now examined substrate recognition by a bacterial (from Borrelia burgdorferi) and an archaeal (from Methanococcus maripaludis) class I lysyl-tRNA synthetase. The genes encoding both enzymes were able to rescue an Escherichia coli strain deficient in lysyl-tRNA synthetase, indicating their ability to functionally substitute for class II lysyl-tRNA synthetases in vivo. In vitro characterization revealed lysine activation and recognition to be tRNA-dependent, a phenomenon previously reported for other class I aminoacyl-tRNA synthetases. More detailed examination of tRNA recognition has shown that class I lysyl-tRNA synthetases recognize the same elements in tRNALys as their class II counterparts; specifically, the discriminator base (N73) and the anticodon serve as recognition elements. The implications of these results for the evolution of Lys-tRNALys synthesis and their possible indications of a more ancient origin for tRNA then aminoacyl-tRNA synthetases will be discussed.