THE human DNA mismatch repair gene homologue, hMSH2, on chromosome 2p is involved in hereditary non-polyposis colon cancer (HNPCC)1,2. On the basis of linkage data, a second HNPCC locus was assigned to chromosome 3p21-23 (ref. 3). Here we report that a human gene encoding a protein, hMLHl (human MutL homologue), homologous to the bacterial DNA mismatch repair protein MutL, is located on human chromosome 3p21.3-23. We propose that hMLHl is the HNPCC gene located on 3p because of the similarity of the hMLHl gene product to the yeast DNA mismatch repair protein, MLH14,5, the coincident location of the hMLHl gene and the HNPCC locus on chromosome 3, and hMLHl missense mutations in affected individuals from a chromosome 3-linked HNPCC family.
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