DNA methylation in xeroderma pigmentosum

DNA methylation was examined in xeroderma pigmentosum (XP) cells. The amount of 5-methylcytosine (mC) in DNA from XP cells was about 70% of that in DNA from normal controls. Southern hybridization analysis showed that the HLA-DR alpha gene in XP lymphocyte B cells was differently methylated from normals, but its expression was apparently unaffected. The methylation of dihydrofolate reductase, a housekeeping gene, was the same as in controls. The revertants to UV resistance from XP fibroblasts recovered a methylation level close to that of normal cells. Results suggested that XP DNA was undermethylated non-randomly, and that DNA methylation might be associated with DNA repair function.