Fine structure mapping of the hypoxanthine-guanine phosphoribosyltransferase (HPRT) gene region of the human X chromosome (Xq26).

The Xq26-q27 region of the X chromosome is interesting, as an unusually large number of genes and anonymous RFLP probes have been mapped in this area. A number of studies have used classical linkage analysis in families to map this region. Here, we use mutant human T-lymphocyte clones known to be deleted for all or part of the hypoxanthine-guanine phosphoribosyltransferase (hprt) gene, to order anonymous probes known to map to Xq26. Fifty-seven T-cell clones were studied, including 44 derived from in vivo mutation and 13 from in vitro irradiated T-lymphocyte cultures. Twenty anonymous probes (DXS10, DXS11, DXS19, DXS37, DXS42, DXS51, DXS53, DXS59, DXS79, DXS86, DXS92, DXS99, DXS100d, DXS102, DXS107, DXS144, DXS172, DXS174, DXS177, and DNF1) were tested for codeletion with the hprt gene by Southern blotting methods. Five of these probes (DXS10, DXS53, DXS79, DXS86 and DXS177) showed codeletion with hprt in some mutants. The mutants established the following unambiguous ordering of the probes relative to the hprt gene: DXS53-DXS79-5'hprt3'-DXS86-DXS10-DXS177 . The centromere appears to map proximal to DXS53. These mappings order several closely linked but previously unordered probes. In addition, these studies indicate that rather large deletions of the functionally haploid X chromosome can occur while still retaining T-cell viability.