The mismatch repair gene MLH1, which is approximately87 kDa in size, is frequently linked to Hereditary Non-Polyposis Colorectal Cancer (HNPCC). This gene was foundto be a site where HNPCC mutations occur often. Thedistinctive changes in microsatellite sequences (RER+phenotype) observed in HNPCC are consistent with the factthat it is a human analogue of the E. coli DNA mismatchrepair gene mutL. Although variants of alternatively splicedtranscripts expressing distinct isoforms have beenidentified, their full-length characteristics remainunknown.