38.2 Transfer RNA Is Extensively Processed

Transfer RNA precursors, which are synthesized by RNA polymerase III, are processed by several means to yield the mature tRNA molecule. As with bacterial tRNAs, nucleotides from the 5′ end on the precursor (the 5′ leader) are cleaved by RNase P, the nucleotides on the 3′ end (the 3′ trailer) are removed by RNase Z, and nucleotides CCA are added by tRNA nucleotidyltransferase (Figure 38.2). Eukaryotic tRNAs are also heavily modified on base and ribose moieties; these modifications are important for function. Many eukaryotic pre-tRNAs also contain an intron, which is removed by an endonuclease, with the resulting products joined by a ligase.

Figure 38.2: Transfer RNA precursor processing. The conversion of a yeast tRNA precursor into a mature tRNA requires the removal of a 14-nucleotide intron (yellow), the cleavage of a 5′ leader (green), the removal of the 3′ trailer (blue), and the attachment of CCA at the 3′ end (red). In addition, several bases are modified.

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