PMS2

PMS2 Full Name

PMS2 postmeiotic segregation increased 2 (S. cerevisiae)

PMS2 Introduction

The PMS2 (PMS1 homolog 2, mismatch repair system component) gene encodes a critical enzyme responsible for maintaining the fidelity of the human genome during DNA replication. As a core component of the DNA mismatch repair (MMR) system, PMS2 functions as the endonuclease that executes the DNA cleavage step essential for correcting replication errors. This gene was initially identified as a human homolog of bacterial mismatch repair genes and has since become one of the most clinically important genes in cancer predisposition. While PMS2 mutations account for approximately 10-15% of Lynch syndrome cases , the gene exhibits distinct features that set it apart from other MMR family members, including a lower cancer penetrance and unique challenges in genetic analysis due to the presence of multiple pseudogenes.

Figure 1. Strcuture of PMS2.

Genomic Location and Structural Organization
The PMS2 gene is located on the short arm of chromosome 7 at position 7p22.1, spanning approximately 38 kilobases of genomic DNA. The gene contains 18 exons that produce a primary transcript encoding a full-length protein of 862 amino acids. A unique challenge in PMS2 genetic analysis stems from the existence of multiple pseudogenes—non-functional copies scattered throughout the genome that share high sequence homology with the functional gene. These pseudogenes complicate molecular diagnostics, as routine testing methods may inadvertently amplify pseudogene sequences, leading to false positive or false negative results. This technical hurdle has historically contributed to under-recognition of PMS2 mutations and necessitates specialized testing approaches for accurate clinical interpretation.

Molecular Function in DNA Mismatch Repair

PMS2 serves as the catalytic endonuclease subunit of the MutL alpha heterodimer, forming a functional complex with its partner protein MLH1. This heterodimer is activated following the recognition of DNA mismatches or insertion-deletion loops by the MutS alpha (MSH2-MSH6) or MutS beta (MSH2-MSH3) complexes. Upon activation, the MutL alpha complex introduces strand breaks in the damaged DNA strand, initiating the excision process that removes the erroneous sequence. The endonucleolytic activity of PMS2 is strictly regulated to ensure that DNA cleavage occurs only at appropriate sites and times. This regulation involves ATP binding and hydrolysis, as well as interactions with proliferating cell nuclear antigen (PCNA) and other replication factors. Through its precise biochemical activity, PMS2 contributes to improving replication fidelity by 100 to 1000-fold, making it indispensable for maintaining genomic stability. Cells deficient in PMS2 exhibit a mutator phenotype characterized by microsatellite instability (MSI)—length alterations in repetitive DNA sequences that serve as hallmarks of MMR deficiency.

Alternate Names for PMS2

PMS2; PMS2 postmeiotic segregation increased 2 (S. cerevisiae); PMSL2, postmeiotic segregation increased (S. cerevisiae) 2; mismatch repair endonuclease PMS2; H_DJ0042M02.9; HNPCC4; PMS1 protein homolog 2; DNA mismatch repair protein PMS2; PMSL2; PMS2CL;

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