The CGA Codon Decoding through tRNA Arg (ICG) Supply Governed by Tad2/Tad3 in Saccharomyces cerevisiae.

The CGA codon is a rare codon in Saccharomyces cerevisiae and is known to be inefficiently decoded by wobble pairing with Arg-tRNA(ICG). The tRNA Arg (ICG) is post-translationally edited from tRNA Arg (ACG) by the anticodon first adenosine deamination enzyme Tad2/Tad3 complex. Experimental consecutive CGA codons cause ribosome stalling to result in reduction of the encoding protein product. In this study, additional supply of tRNA Arg (ACG) genes that produce decoding Arg-tRNA(ICG) promoted the product level from the CGA12-luc reporter, revealing that the product reduction is essentially due to inefficient decoding and deficiency in the tRNA supply. The mature tRNA Arg (ICG) and the precursor tRNA Arg (ACG) ratios examined for cellular tRNA fraction revealed that the tRNA Arg (ICG) ratio is maintained at less than 30%, and is responsive to the Tad2/Tad3, expression level.