NifU-like proteins are a highly conserved protein that serves as the scaffold for assembly of Fe-S clusters. Chloroplastic NifU-like proteins have tandem NifU like domains, named domain I and domain II. Although the amino acid sequences of these domains are very similar to each other, the predicted functional region for the Fe-S cluster assembly, the CXXC motif, exists only in domain I. The structure of the domain II of chloroplastic NifU-like protein OsNifU1A has an alpha-beta sandwich structure containing two alpha helices located on one side of the beta-sheet. The electrostatic surface potential of OsNifU1A domain II is predominantly positively charged. Chloroplastic NifU-like proteins are targeted to ferredoxin for transferring the Fe-S cluster. The ferredoxin presents an overall negatively charged surface, which may evoke an electrostatic association with OsNifU1A domain II.