MMS19 is a 1,030 amino acid nuclear protein containing seven HEAT repeats that belongs to the MET18/MMS19 family. Via its interactions with TFIIH p80 and TFIIH p89 helicases, MMS19 plays a role in nucleotide excision repair (NER) and RNA polymerase II (Pol II) transcription. MMS19 may also function as a transcriptional coactivator of estrogen receptor. While ubiquitously expressed, highest levels of MMS19 have been found in testis. At least five distinct MMS19 protein isoforms exist, which are produced by alternative splicing events. The gene encoding MMS19 maps to human chromosome 10q24.1, and is associated with the risk of pancreatic cancer.