Practice question

All mature tRNAs require conserved CCA terminal trinucleotide at 3' end where amino acid attaches via ester linkage. In most bacteria and eukaryotes, CCA is absent from tRNA gene and added post-transcriptionally by ATP(CTP):tRNA nucleotidyltransferase, CCA-adding enzyme. This enzyme binds T-loop and acceptor stem, sequentially polymerizing C-C-A using CTP and ATP. It also surveys tRNA quality, adding CCA to correctly folded tRNAs and engaging in repair cycles where damaged termini are excised and resynthesized, ensuring translational competence. This refined regulation supports accurate ribosomal assembly, quality control and translational fidelity under diverse physiological conditions and growth states.