RADIATION HYBRIDS FOR THE PROXIMAL LONG ARM OF THE X-CHROMOSOME AND THEIR USE IN THE DERIVATION OF AN ORDERED SET OF COSMID MARKERS FROM A DEFINED SUBREGION IN PROXIMAL XQ13.1

We have defined a radiation hybrid panel for X411-q22 characterized wi th 20 DNA markers and shown how the panel can be used in conjunction w ith Alu-PCR and a gridded X-specific cosmid library to isolate cosmids from a preselected subregion. We used Alu-PCR products derived from t wo radiation hybrids, IHB2-B30 and IHB1-A12, sharing a segment in prox imal Xq13.1, containing DXS453 to CCG1, as the only human component in common. Used as probes, these Alu-PCR products identified 39 cosmids on the gridded X-cosmid libraries that were positive for both probes. The target specificity of the derived cosmids,vas very high, 11 of 13 cosmids tested mapped to the region of fragment overlap in the hybrids , as was determined by two translocation breakpoints bordering most of the target interval. Accounting for a redundancy of four in the libra ries, the isolated 39 cosmids should correspond to about 10 independen t loci derived from the region of fragment overlap defined by these ra diation hybrids. In addition, a subset of five radiation hybrids havin g breakpoints in the target region could be used to further subdivide the 11 cosmids into an ordered set of five submapping intervals of Xq1 3.1.