Human CCA-adding enzyme is able to repair damaged CCA ends of tRNAs.
(A) Total HeLa tRNAs and (B) internally radioactively labeled yeast tRNAPhe 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  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 (Figure 1A, schematic inset). tRNAPhe lacking the terminal 3′-adenosine (tRNAPheCC) served as a control. The numbers on the left denote the DNA ladder in nt.