DENOVO METHYLATION CAUSES A TISSUE-SPECIFIC POLYMORPHIC ECORI PATTERNAT THE HUMAN EPIDERMAL GROWTH-FACTOR RECEPTOR GENE

A novel restriction polymorphism, probably due to tissue-specific meth ylation, has been identified at the human epidermal-growth-factor-rece ptor (EGF-R) gene. DNA isolated from smooth muscle showed altered EcoR I restriction bands when hybridized with different fragments of the EG F-R cDNA. These bands were absent in brain or leucocyte DNA samples fr om the same individuals. Three restriction sites, partly resistant to cleavage by EcoRI, were characterized in muscle DNA which were not clu stered but instead were scattered along the gene. The flanking sequenc es of one of these resistant EcoRI sites were determined. This specifi c EcoRI site was followed by a 3'-guanosine generating a methylatable EcoRI sequence. This suggests that the failure to digest to completion these EcoRI sites was due to modification by methylation. In addition , we noted that EcoRI sites were affected at both alleles, indicating that -de novo methylation changes, and not methylation events related to genomic imprinting, would cause the muscle-specific EcoRI pattern. Also abnormal restriction fragments with Xhal were observed in muscle DNA. A large number of unrelated muscle DNA samples have been analysed , and all of them displayed an identical EcoRI polymorphic pattern. su ggesting that DNA modification by de novo methylation events could be functionally relevant.