tRNA nucleotidyltransferase involved in the synthesis of the tRNA CCA terminus. Adds the two cytidine residues to tRNA. a tRNA precursor + 2 CTP = a tRNA with a 3' CC end + 2 diphosphate Adopts a seahorse-like shape and consists of four domains: head, neck, body, and tail. Belongs to the tRNA nucleotidyltransferase/poly(A) polymerase family.