tRNA nucleotidyltransferase involved in the synthesis of the tRNA CCA terminus. In contrast to what is usually observed in eukaryotes for which one enzyme synthesizes the whole tRNA CCA terminus, in S.pombe, cca1 specifically adds two cytidine residues to a tRNA substrate lacking this sequence while cca2 specifically adds the terminal adenosine residue thereby completing the CCA sequence. a tRNA precursor + 2 CTP = a tRNA with a 3' CC end + 2 diphosphate Cca1 contains two alpha-helices (His-81 to Thr-86 and Glu-479 to Asp-484) and a beta-sheet (His-120 to Lys-131) that are not seen in cca2, suggesting that cca1 has lost A-adding activity because this beta-sheet reduces the flexibility of the loop (Asp-122 to Glu-139) as compared to CCA- and A-adding enzymes. The ERhxxExxxhh motif (residues 231-241) has been suggested to serve to distinguish between A-adding and CC-adding proteins as A-adding enzymes have a small amino acid in the first position while CC-adding enzymes have an E in the first position. Belongs to the tRNA nucleotidyltransferase/poly(A) polymerase family.