Key component of the cytosolic iron-sulfur protein assembly (CIA) complex, a multiprotein complex that mediates the incorporation of iron-sulfur cluster into extramitochondrial Fe/S proteins (PubMed:17937914, PubMed:23891004). As a CIA complex component, interacts specifically with CIAO2A or CIAO2B and MMS19 to assist different branches of iron-sulfur protein assembly, depending of its interactors. The complex CIAO1:CIAO2B:MMS19 binds to and facilitates the assembly of most cytosolic-nuclear Fe/S proteins. CIAO1:CIAO2A specifically matures ACO1 and stabilizes IREB2 (PubMed:23891004). Seems to specifically modulate the transactivation activity of WT1 (PubMed:9556563). As part of the mitotic spindle-associated MMXD complex it may play a role in chromosome segregation (PubMed:20797633). Component of the CIA complex (PubMed:22678361, PubMed:22678362, PubMed:23585563). Interacts with CIAO2A and forms a complex with CIAO2B and MMS19; the interactions with CIAO2A and CIAO2B are mutually exclusive (PubMed:22683786, PubMed:23891004, PubMed:23585563). Interacts with CHD1L, ERCC2, IREB2 and POLD1 (PubMed:23891004). Component of the MMXD complex, which includes CIAO1, ERCC2, CIAO2B, MMS19 and SLC25A5 (PubMed:20797633). Interacts with WT1 (PubMed:9556563). Interacts with CIAO3 (PubMed:23585563). Interacts (via LYR motif) with HSC20 (PubMed:29309586). 'Ciao' means 'bridge' in Chinese. Belongs to the WD repeat CIA1 family.