Chromatin structure of active and inactive human X-linked phosphoglycerate kinase gene.

We have carried out a comparative analysis of DNase I sensitivity of the active and inactive X-linked phosphoglycerate kinase (Pgk) genes in human lymphoblast and fibroblast cultured cells. Three DNase I-sensitive regions were detected: a 5' hypersensitive site, a sensitive region in the interior of the gene and a 3' slightly sensitive site which we previously reported and have now mapped with some precision. A comparison of these sensitive sites in single and multiple X cell lines indicates that the sensitive sites are unique to the active X chromosome. A similar study of an X-linked Pgk pseudogene shows no difference in DNase I sensitivity between the pseudogenes on the active and inactive X chromosomes. These latter results imply that sex chromatin does not confer a unique level of DNase I resistance to DNA on the inactive X chromosome. The exact role of sex chromatin in differential DNase I sensitivity of genes on the inactive and active X chromosomes is discussed.