Pulsed-field map of Xq13 in the region of the human X inactivation center.

We have used human/mouse hybrid cell lines to derive a pulsed-field map of the Xq13 region of the human X chromosome, in the vicinity of the X inactivation center (XIC). We have mapped nine loci within two separate clusters (I and II). Cluster I contains three loci (DXS227, XIST, and DXS128) linked within 1700 kb. This cluster also includes the breakpoint of a translocated X;14 chromosome used to define the proximal border of the XIC region. Cluster II covers an additional 1800 kb and physically links six loci (DXS56, DXS171, DXS325, DXS347, DXS356, and DXS441) located between the XIC and the genes for Menkes disease (MNK) and PGK1. Maps of cluster I loci derived from active (Xa) or inactive (Xi) X chromosomes differed, presumably due to methylation differences between the Xa and Xi. This map provides a basis for examining the organization of the Xq13.2-q13.3 region, in and around the XIC, and will assist in the further cloning of expressed sequences from this region.