Small angle X-ray scattering (SAXS) is a valuable technique for the study of flexible, low compactness macromolecules in solution, which has already been successfully used to characterize N TAIL ). Therefore, we used SAXS to study the N TAIL -XD complex. To this endeavor, we cloned, expressed, and purified from the soluble fraction of Escherichia coli an N-terminally histidine-tagged form of N TAIL (i.e., N TAILHN ) (data not shown). The identity of the recombinant products was confirmed by immunoprecipitation (IP) studies using anti-N Cl25 and anti-hexahistindine tag monoclonal antibodies (mAbs) (data not shown).