Human CCA-adding enzyme is able to repair damaged CCA ends of tRNAs.

<p>(A) Total HeLa tRNAs and (B) internally radioactively labeled yeast tRNA<sup>Phe</sup> were incubated successively with angiogenin and human CCA-adding enzyme. Subsequently to the angiogenin treatment (4 h), T4 polynucleotide kinase (PNK) (45 min) was added which converts the 2′,3′-cyclophosphate ends <a href="" target="_blank">[42]</a> generated by the angiogenin cleavage to free 3′OH. After purification tRNAs were subjected to treatment with the CCA-adding enzyme (30 min). The 3′-CCA end integrity of the HeLa tRNAs was determined with the fluorescent oligonucleotide (<a href="" target="_blank">Figure 1A</a>, schematic inset). tRNA<sup>Phe</sup> lacking the terminal 3′-adenosine (tRNA<sup>Phe</sup>CC) served as a control. The numbers on the left denote the DNA ladder in nt.</p>