Involved in iron-sulfur (Fe-S) cluster assembly. May act as a regulator of Fe-S biogenesis. Interacts with IscS. Certain pairs of proteins can bind simultaneously to IscS; IscS-IscU-CyaY complexes can be isolated in vitro, but (IscS-TusA-CyaY) complexes cannot. Belongs to the frataxin family.