Is able to transfer iron-sulfur clusters to apo-ferredoxin. Multiple cycles of [2Fe2S] cluster formation and transfer are observed, suggesting that IscA acts catalytically. Recruits intracellular free iron so as to provide iron for the assembly of transient iron-sulfur cluster in IscU in the presence of IscS, L-cysteine and the thioredoxin reductase system TrxA/TrxB. Binds 2 iron ions per dimer. The dimer may bind additional iron ions. Homodimer; may form tetramers and higher multimers. Belongs to the HesB/IscA family.