The primary structure of transcription factor TFIIIA has 12 consecutive repeats

Analysis of the amino acid sequence of transcription factor TFIIIA from Xenopus laevis reveals the presence of 12 repeating structures, each about 30 residues in length. These segments have been aligned and their secondary structure predicted. The repeats each contain two invariant cysteines and two invariant histidines, perhaps to coordinate a zinc cation. Possible nucleic acid interaction modes are discussed.