Catalyzes the addition and repair of the essential 3'-terminal CCA sequence in tRNAs without using a nucleic acid template. Adds these three nucleotides in the order of C, C, and A to the tRNA nucleotide-73, using CTP and ATP as substrates and producing inorganic pyrophosphate. a tRNA precursor + ATP + 2 CTP = a tRNA with a 3' CCA end + 3 diphosphate The KM for ATP is much higher than 30 uM. Optimum pH is about 9. Active from pH 7 to 10. Optimum temperature is 70 degrees Celsius. Inactive at 37 degrees Celsius. Homodimer. Forms a tetramer upon binding two tRNAs. However, tRNA-induced tetramer formation is not required for CCA addition. A single active site specifically recognizes both ATP and CTP and is responsible for their addition. Belongs to the tRNA nucleotidyltransferase/poly(A) polymerase family. Archaeal CCA-adding enzyme subfamily.