Allele-specific methylation of the human c-Ha-ras-1 gene.

The methylation status of individual c-Ha-ras-1 alleles in human cells was measured by Hpall/Mspl analysis of a polymorphic (VTR) region. The gene was extensively methylated in leukocytes and sperm, with the former exhibiting a highly specific methylation pattern. Individual ras alleles were differentially methylated at the VTR region in fetal fibroblasts and immortal cell lines. A new polymorphism in the 5'-flanking region of the gene was also detected. The presence or absence of an Xhol site showed a striking and complete concordance with the length of the VTR region and suggested that the site had been lost by a previous allele-specific mutation.