i-tRAP (individual tRNA acylation PCR): a convenient method for selective quantification of tRNA charging

Each transfer RNA (tRNA) is aminoacylated (charged) with a genetic codon-specific amino acid at its 3′ end. Charged tRNAs are primarily used for translation, whereas fluctuations in charged tRNA fractions are known to reflect cellular response to stress. Here we report the development of individual tRNA-acylation using PCR (i-tRAP), a convenient PCR-based method that can specifically quantify the individual tRNA charging ratio. In this i-tRAP method, demethylases remove base methylations which are problematic for reverse transcription reaction, and β-elimination reaction specifically removes the 3′ end of adenine residue in uncharged tRNA. Subsequent TaqMan MGB qRT-PCR can distinguish between cDNA of charged tRNA and uncharged tRNA. By using this method, we revealed that the charging ratio of tRNA(Gln)(CUG) was changed in response to amino acid starvation and also the charging ratio of tRNA(Gln)(CUG) in senescent cells was lower than in young cells under starvation conditions. i-tRAP can be applicable to the quantification of the charging ratio of various tRNAs, and provides a simple and convenient method for analyzing tRNA charging.