Cytidine in the anticodon second position (position 35) and G or U in position 36 of tRNAArg are required for aminoacylation by arginyl-tRNA synthetase (ArgRS) from Escherichia coli. Nevertheless, an arginine-accepting amber suppressor tRNA with a CUA anticodon (FTOR1D26) exhibits suppression activity in vivo [McClain, . & Foss, K. (1988) Science, 241, 1804 –1807]. By an in vitro kinetic study with mutagenized tRNAs, we showed that the arginylation of FTOR1D26 involves C34 and U35, and that U35 can be replaced by G without affecting the activity. Thus, the positioning of the essential nucleotides for the arginylation is shifted to the 50.
