Key component of the cytosolic iron-sulfur protein assembly (CIA) complex, a multiprotein complex that mediates the incorporation of iron-sulfur cluster into apoproteins specifically involved in DNA metabolism and genomic integrity. In the CIA complex, MMS19 acts as an adapter between early-acting CIA components and a subset of cellular target Fe/S proteins such as ERCC2/XPD, FANCJ and RTEL1, thereby playing a key role in nucleotide excision repair (NER), homologous recombination-mediated double-strand break DNA repair, DNA replication and RNA polymerase II (POL II) transcription. As a CIA complex component and in collaboration with CIAO1 and CIAO2, binds to and facilitates the assembly of most cytosolic-nuclear Fe/S proteins. As part of the mitotic spindle-associated MMXD complex, plays a role in chromosome segregation, probably by facilitating iron-sulfur cluster assembly into ERCC2/XPD. Together with CIAO2, facilitates the transfer of Fe-S clusters to the motor protein KIF4A, which ensures proper localization of KIF4A to mitotic machinery components to promote the progression of mitosis. Indirectly acts as a transcriptional coactivator of estrogen receptor (ER), via its role in iron-sulfur insertion into some component of the TFIIH-machinery. Component of the CIA complex. In the CIA complex, interacts directly with CIAO2B and CIAO3. Component of the MMXD complex, composed of CIAO1, ERCC2, CIAO2B, MMS19 and SLC25A5. Interacts with CIAO2B; the interaction is direct. Interacts with ERCC2/XPD; the interaction is direct. Interacts with ERCC3/XPB and NCOA3/RAC3. Interacts with RTEL1; the interaction mediates the association of RTEL1 with the CIA complex. Interacts with BRIP1. Interacts with KIF4A; the interaction facilitates the transfer of Fe-S clusters to KIF4A to ensure proper localization of KIF4A to the mitotic machinery components. Interacts with CCDC117; the interaction is indirect (By similarity). Ubiquitinated; undergoes 'Lys-48'-linked polyubiquitination. Belongs to the MET18/MMS19 family.