Footprinting of Protein Interactions by Tritium Labeling

A new footprinting method for mapping protein interactions has been developed, using tritium as a radioactive label. As residues involved in an interaction are less labeled when the complex is formed, they can be identified via comparison of the tritium incorporation of each residue of the bound protein with that of the unbound one. Application of this footprinting method to the complex formed by the histone H3 fragment H3122−135 and the protein hAsf1A1−156 afforded data in good agreement with NMR results.