The processing of tRNA. Transfer RNAs are trimmed at the 5′ and 3′ ends by RNase P and RNase D, respectively. Shown here is the processing of tRNATyr. The CCA trinucleotide is added to the 3′ end, and some bases are modified to provide stability and enhance the functioning of the mature tRNA. In some eukaryotic tRNAs, introns are excised during processing.