Evidence that hMLH3 functions primarily in meiosis and in hMSH2-hMSH3 mismatch repair.

The MutS (MSH) and MutL (MLH) homologs are conserved proteins that function in mismatch repair (MMR) and meiosis. We examined mRNA and protein expression of hMLH3 compared to other human MSH and MLH in a panel of human tissues and the HeLa cell line. Quantitative PCR suggests that MSH and MLH transcripts are expressed ubiquitously. hMLH3 mRNA is present at low levels in numerous tissues. Protein expression appears to correlate with a threshold of mRNA expression with hMLH3 present at high levels in testis. In addition, we have found and mapped interactions between hMLH1 and hMLH3 with hMSH3. These data are consistent with yeast studies and suggest a role for hMLH3 in meiosis as well as hMSH2-hMSH3 repair processes and little if any role in Hereditary Non-Polyposis Colorectal Cancer (HNPCC).