The PMS1 gene is composed of 13 exons spanning in a region of 93056 bp.

The transcribed mRNA has 3032 bp

Amino acids: 932. Molecular Weight: 105830 Daltons. PMS1 is a protein involved in the mismatch repair process after DNA replication.

PMS1 binds to MLH1 to form a heterodimer, although MLH1 can also bind to PMS2 or MLH3. Although MLH1/PMS2 binds to the heteroduplexes MutSa (composed of MSH2 and MSH6) or MutSβ (composed of MSH2 and MSH3), which recognize DNA lesions, it remains to be demonstrated the involvement of the MLH1/PMS1 heterodimer in the mismatch repair process, despite that the heterodimer MLH1/PMS2 is responsible for the recruitment of the proteins needed for the excision and repair synthesis.

PMS1 is homologue to the bacterial MutL gene and to the Mlh2 gene in yeasts.

A truncating germline mutation of PMS1 was found in one HNPCC patient. Nevertheless, a MSH2 mutation was found in this family, which was the only one that co-segregated with colon cancer. In addition, no more HNPCC patients have been found with mutations in this gene, and PMS1 -/- mice show no discernible phenotype. So there is no evidence that PMS1 mutations predispose to HNPCC.