A yeast arginine specific tRNA is a remnant aspartate acceptor

摘要

High specificity in aminoacylation of transfer RNAs (tRNAs) with the help of their cognate aminoacyl-tRNA synthetases (aaRSs) is a guarantee for accurate genetic translation. Structural and mechanistic peculiarities between the different tRNA/aaRS couples, suggest that aminoacylation systems are unrelated. However, occurrence of tRNA mischarging by non-cognate aaRSs reflects the relationship between such systems. In Saccharomyces cerevisiae, functional links between arginylation and aspartylation systems have been reported. In particular, it was found that an in vitro transcribed tRNA(Asp) is a very efficient substrate for ArgRS. In this study, the relationship of arginine and aspartate systems is further explored, based on the discovery of a fourth isoacceptor in the yeast genome, tRNA(4)(Arg). This tRNA has a sequence strikingly similar to that of tRNA(Asp) but distinct from those of the other three arginine isoacceptors. After transplantation of the full set of aspartate identity elements into the four arginine isoacceptors, tRNA(4)(Arg) gains the highest aspartylation efficiency. Moreover, it is possible to convert tRNA(4)(Arg) into an aspartate acceptor, as efficient as tRNA(Asp), by only two point mutations, C38 and G73, despite the absence of the major anticodon aspartate identity elements. Thus, cryptic aspartate identity elements are embedded within tRNA(4)(Arg). The latent aspartate acceptor capacity in a contemporary tRNA(Arg) leads to the proposal of an evolutionary link between tRNA(4)(Arg) and tRNA(Asp) genes.