Identification of hMutLbeta, a heterodimer of hMLH1 and hPMS1.
hMLH1 and hPMS2 function in postreplicative mismatch repair in the form of a heterodimer referred to as hMutLalpha. Tumors or cell lines lacking this factor display mutator phenotypes and microsatellite instability, and mutations in the hMLH1 and hPMS2 genes predispose to hereditary non-polyposis colon cancer. A third MutL homologue, hPMS1, has also been reported to be mutated in one cancer-prone kindred, but the protein encoded by this locus has so far remained without function. We now show that hPMS1 is expressed in human cells and that it interacts with hMLH1 with high affinity to form the heterodimer hMutLbeta. Recombinant hMutLalpha and hMutLbeta, expressed in the baculovirus system, were tested for their activity in an in vitro mismatch repair assay. While hMutLalpha could fully complement extracts of mismatch repair-deficient cell lines lacking hMLH1 or hPMS2, hMutLbeta failed to do so with any of the different substrates tested in this assay. The involvement of the latter factor in postreplicative mismatch repair thus remains to be demonstrated.
Räschle
M
M
Institute of Medical Radiobiology, University of Zürich August Forel-Strasse 7, CH-8008 Zürich, Switzerland.
Marra
G
G
Nyström-Lahti
M
M
Schär
P
P
Jiricny
J
J
D048868:Adaptor Proteins, Signal Transducing; D000251:Adenosine Triphosphatases; D000818:Animals; D020137:Base Pair Mismatch; D002352:Carrier Proteins; D002460:Cell Line; D004260:DNA Repair; D045643:DNA Repair Enzymes; D004268:DNA-Binding Proteins; D019281:Dimerization; D006801:Humans; D000070976:Mismatch Repair Endonuclease PMS2; D000070957:MutL Protein Homolog 1; D000070956:MutL Proteins; D009363:Neoplasm Proteins / Q000235:genetics / Q000378:metabolism*; D009687:Nuclear Proteins; D018411:Spodoptera
D048868:Adaptor Proteins, Signal Transducing; D002352:Carrier Proteins; D004268:DNA-Binding Proteins; C501486:MLH1 protein, human; D009363:Neoplasm Proteins; D009687:Nuclear Proteins; C088996:PMS1 protein, human; D000251:Adenosine Triphosphatases; C094934:PMS2 protein, human; D000070976:Mismatch Repair Endonuclease PMS2; D000070957:MutL Protein Homolog 1; D000070956:MutL Proteins; D045643:DNA Repair Enzymes