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 (PubMed:29848660). In the CIA complex, MMS19 acts as an adapter between early-acting CIA components and a subset of cellular target iron-sulfur 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 (PubMed:22678362, PubMed:22678361, PubMed:29225034, PubMed:23585563). As part of the mitotic spindle-associated MMXD complex, plays a role in chromosome segregation, probably by facilitating iron-sulfur (Fe-S) cluster assembly into ERCC2/XPD (PubMed:20797633). 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 (PubMed:29848660). Indirectly acts as a transcriptional coactivator of estrogen receptor (ER), via its role in iron-sulfur insertion into some component of the TFIIH-machinery (PubMed:11279242). Component of the CIA complex (PubMed:22678362, PubMed:22678361, PubMed:23585563). In the CIA complex, interacts directly with CIAO2B and CIAO3 (PubMed:23585563). Component of the MMXD complex, composed of CIAO1, ERCC2, CIAO2B, MMS19 and SLC25A5 (PubMed:20797633). Interacts with CIAO2B; the interaction is direct (PubMed:20797633). Interacts with ERCC2/XPD; the interaction is direct (PubMed:11071939, PubMed:23585563). Interacts with ERCC3/XPB and NCOA3/RAC3 (PubMed:11071939, PubMed:11279242). Interacts with RTEL1; the interaction mediates the association of RTEL1 with the CIA complex (PubMed:22678361, PubMed:23585563). Interacts with BRIP1 (PubMed:23585563). 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 (PubMed:29848660). Interacts with CCDC117; the interaction is indirect (PubMed:30742009). In mitosis, enriched on centrosomes during prophase, localizes to the spindle during metaphase and surrounds compacted spindle midzone microtubules during telophase. Ubiquitously expressed with higher expression in testis. Ubiquitinated; undergoes 'Lys-48'-linked polyubiquitination by MAGEF1-NSMCE1 ubiquitin ligase complex leading to proteasomal degradation. May be produced at very low levels due to a premature stop codon in the mRNA, leading to nonsense-mediated mRNA decay. May be produced at very low levels due to a premature stop codon in the mRNA, leading to nonsense-mediated mRNA decay. Belongs to the MET18/MMS19 family. Wrong choice of CDS. Truncated N-terminus. Wrong choice of CDS. Truncated N-terminus.