Postreplicative Mismatch Repair and its Malfunction in Hereditary Colon Cancer
Seven human genes encoding mismatch repair proteins have been identified to date: hMSH2, hMSH3, hMSH6, hMLH1, hMLH3, hPMS1 and hPMS2. Our goal is to elucidate the roles of the products of the above genes in the mismatch repair process, which is thought to involve, in addition to the above polypeptides, also PCNA, RFC, RPA, polymerase-d, a DNA-helicase and 5'-3' as well as 3'-5' exonuclease(s). Our initial studies focused on the heterodimeric mismatch recognition factors hMSH2/hMSH6 and hMSH2/hMSH3, referred to as hMutS-a, and hMutS-b respectively. These factors were expressed in the baculovirus system and their ability to complement extracts of mismatch repair - deficient cell lines was assessed. Later studies examined their enzymatic activity and mode of action. Recently we have been focusing on the ATPase activity of the hMLH1/hPMS2 heterodimer, referred to as hMutL-a. We are currently studying higher order protein/protein interactions, in particular those of hMutL-a.with hMutS-a bound to mismatch-containing DNA. To this end, we are utilising mismatch repair gene variants carrying mutations that affect the nucleotide cofactor or DNA binding sites, or mutations found in kindreds with the common cancer predisposition syndrome, hereditary non-polyposis colon cancer (HNPCC).
Patrick Dufner, Ingram Iaccarino, Giancarlo Marra, Minna Nyström-Lahti, Claudia Perrera, Markus Räschle and Josef Jiricny
Institute of Medical Radiobiology, August Forel-Strasse 7,