MMS19 nucleotide excision repair protein homolog is a protein that in humans is encoded by the MMS19 gene.

Function: May play a role in nucleotide excision repair (NER) and RNA polymerase II (POL II) transcription by interacting with ERCC2/XPD and ERCC3/XPB helicases, both subunits of NER-transcription factor TFIIH. May also function as a transcriptional coactivator of estrogen receptor (ER). May be involved in regulation of ER activity by bridging TFIIH with ER or may facilitate TFIIH-mediated phosphorylation of ER in specific promoters and cell types. As part of the mitotic spindle-associated MMXD complex it plays a role in chromosome segregation.