Active X Chromosome DNA is Unmethylated at Eight CCGG Sites Clustered in a Guanine-Plus-Cytosine-Rich Island at the 5′ End of the Gene for Phosphoglycerate Kinase

Abstract

The 5' control region and first exon for human X-chromosome-linked phosphoglycerate kinase is contained in a G + C-rich island. We measured methylation at all HpaII sites in this 5' region of leukocyte DNA. By use of a blotting procedure that allows analysis of small DNA fragments, we found that the HpaII sites are entirely methylated when from an inactive X chromosome and entirely unmethylated when from an active one. In contrast, methylation of HpaII sites in more downstream regions of the gene is essentially the same in active and inactive X chromosomes.