ThePMS2gene encodes a protein that is involved in DNA mismatch repair and is mutated in a subset of patients with hereditary nonpolyposis colon cancer (HNPCC). The previously publishedPMS2cDNA sequence lacks an upstream in-frame stop codon preceding the presumptive initiating methionine. To evaluate the 5′ terminus of thePMS2coding region further, we isolated additional cDNA clones, RT-PCR products, and the corresponding 5′ genomic segment of thePMS2locus. ThePMS2gene transcripts were found to have heterogeneous but colinear 5′ termini, one of which contained an in-frame termination codon preceding the initiating methionine. In addition, a novel gene encoding a 34.5-kDa polypeptide was found to initiate transcriptionally withinPMS2from the opposite strand.
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