IDENTIFICATION OF YAC AND COSMID CLONES ENCOMPASSING THE ZFX-POLA REGION USING IRRADIATION HYBRID CELL-LINES

The human Xp21.3-p22.1 region is poorly mapped relative to other X chr omosome regions. To target cosmid and YAC clones specifically from Xp2 1.3-p22.1 for rapid contig construction, a hybridization-based screeni ng approach using irradiation hybrids has been used. ALu-PCR products generated from hybrid lines containing small overlapping fragments fro m Xp21-p22 were hybridized to an X chromosome cosmid library, and cosm ids predicted by their hybridization pattern to map to the region of i nterest were analyzed by fluorescence in situ hybridization (FISH). Hy bridization of the cosmids in pools to gridded YAC libraries identifie d 15 YACs, which were verified and tested for chimerism by FISH. Cosmi d content analysis of the YACs defined two contigs, one with 12 YACs c overing about 1.5 Mb and one with 3 YACs. Five YACs from the 12-YAC cl uster had been previously recognized by DNA polymerase alpha (POLA). Z FX identified a single YAC; hence, the physical linkage of ZFX and POL A was demonstrated within the contig. Four YACs had been isolated prev iously with ZFX and these extend the contig to 2 Mb. Restriction mappi ng of several YACs demonstrates that ZFX and POLA are about 700 kb apa rt, a distance similar to that reported in the mouse between Zfx and P olo. The order of these two loci and two additional loci identified by homologous mouse linking clones was found to be conserved between hum an and mouse: tel-ZFX-DXCrc57-DXCrc140-POLA-cen. We have shown that YA C contigs can be rapidly constructed from targeted regions without the need for time-consuming YAC end rescue and chromosomal walking. This approach also generates a series of ordered cosmids, which is particul arly valuable for marker generation in regions in which disease gene l ocalization is hampered by low marker density. (C) 1994 Academic Press , Inc.