Archaeal CCA-adding enzyme builds and repairs the 3'-end of tRNA [1-4]. This is the C-terminal domain (tail) of CCA-adding enzyme, which serves as a ruler to ensure that only tRNAs and tRNA-like transcripts are substrates for the enzyme and also contributes to the discrimination between stable and unstable RNA substrates [4].

1: Crystal structures of an archaeal class I CCA-adding enzyme and its nucleotide complexes. Xiong Y, Li F, Wang J, Weiner AM, Steitz TA; Mol Cell. 2003;12:1165-1172. PMID:14636575

2: Molecular basis for maintenance of fidelity during the CCA-adding reaction by a CCA-adding enzyme. Toh Y, Numata T, Watanabe K, Takeshita D, Nureki O, Tomita K; EMBO J. 2008;27:1944-1952. PMID:18583961

3: How the CCA-adding enzyme selects adenine over cytosine at position 76 of tRNA. Pan B, Xiong Y, Steitz TA; Science. 2010;330:937-940. PMID:21071662

4: On-enzyme refolding permits small RNA and tRNA surveillance by the CCA-adding enzyme. Kuhn CD, Wilusz JE, Zheng Y, Beal PA, Joshua-Tor L; Cell. 2015;160:644-658. PMID:25640237