10.6: tRNA Processing in Eukaryotic Nuclei

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RNA polymerase III also transcribes tRNA genes from internal promoters, but unlike the 5S rRNA genes, tRNA genes tend to cluster in the genome (Figure. 10.23).

Screen Shot 2022-05-19 at 11.39.54 PM.png — Figure 10.23: Genes encoding tRNAs for different amino acids are organized in characteristic gene-clusters, with genes oriented (i.e., transcribed) in opposite directions.

Also unlike 5S rRNA genes, tRNA primary transcripts are processed by trimming, the enzymatic addition of a 3’-terminal-C-C-A triplet, and the modification of bases internal to the molecule. A yeast tRNA showing these modifications is illustrated in Figure 10.24.

Screen Shot 2022-05-19 at 11.40.53 PM.png — Figure 10.24: Structure of a processed, mature yeast tRNA, trimmed at 3' and 5' ends with an enzymatically added three-nucleotide (C-C-A amino acid attachment site and modified bases.

The yeast tRNA folds into several hairpin loops based on internal H-bond formation between complementary bases in the molecule. An amino acid specific for the tRNA will be enzymatically added to the A residue of the 3’ terminal -C-C-A.

200-2 tRNA Transcription and Processing

CHALLENGE

What do you think determines which amino acid will bind to which tRNA?