Identification and functional characterization of the promoter region of the human MSH6 gene

Postreplicative mismatch repair (MMR) corrects polymerase errors arising du ring DNA replication. Consistent with this role, the Saccharomyces cerevisi ae MMR genes MSH2, MSH6, and PMS1 were reported to be transcriptionally upr egulated during late G(1) phase of the cell cycle. Surprisingly, despite th e high degree of conservation of the MMR system in evolution, the human MMR genes studied to date, MSH2, MLH1, and PMS2, appear to be transcribed from classical housekeeping promoters, and the amounts of the polypeptides enco ded by them fluctuate little during the cell cycle. Only the amounts of the 160-kDa MSH6 protein were reported to vary, both during development and fo llowing stimulation of cell growth. Moreover, transcription of this gene wa s found to be downregulated by CpG methylation of the promoter region in a subset of clones treated with alkylating agents. In an attempt to understan d the molecular basis underlying these phenomena, we isolated the S' region of the MSH6 gene and subjected it to functional analysis. We now show that the MSH6 gene is also transcribed from a classical housekeeping gene promo ter. Despite housing putative binding sites for the transcription factors A PI, NF-KB, and MTF-I, the MSH6 promoter failed to respond to ionizing radia tion or heavy metals. Interestingly, MSH6 transcription was upregulated dur ing late G, phase, even though the levels of the protein remained essential ly constant during the cell cycle. (C) 2002 Wiley-Liss, Inc.