NMR is a useful tool to identify the protein-protein interaction surfaces on two interacting proteins. In this experiment the HSQC spectrum of RPA70N was determined in the absence (black) or presence (red) of ATRIP. The shifts in the spectra correspond to perturbations in RPA amino acids that make contact with ATRIP. Mapping of the chemical shifts onto the RPA70N crystal structure reveals that ATRIP binds in a cleft of the RPA70N. These experiments were done in collaboration with Walter Chazin and Siva Vaithiyalingam in the Center for Structural Biology at Vanderbilt.