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. A transposon insertion between iscA and hscB prevents colonization of the nematode Steinernema carpocapsae. The insertion disrupts cotranscription of iscA and hscB but does not reduce hscBA expression, suggesting that coordinated expression of the isc-hsc-fdx locus is required for colonization. Belongs to the HesB/IscA family.