Discovery of Zinc fingers, a protein structural motif. "Zinc fingers were first identified in a study of transcription in the African clawed frog, Xenopus laevis in the laboratory of Aaron Klug. A study of the transcription of a particular RNA sequence revealed that the binding strength of a small transcription factor (transcription factor IIIA; TFIIIA) was due to the presence of zinc-coordinating finger-like structures.^[6] Amino acid sequencing of TFIIIA revealed nine tandem sequences of 30 amino acids, including two invariant pairs of cysteine and histidine residues. Extended x-ray absorption fine structure confirmed the identity of the zinc ligands: two cysteines and two histidines.^[5] The DNA-binding loop formed by the coordination of these ligands by zinc were thought to resemble fingers, hence the name" (Wikipedia article on Zinc finger, accessed 7-22).