A rodent‐human hybrid containing Xq24‐qter translocated to a hamster chromosome expresses the Xq27 folate‐sensitive fragile site

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Abstract
A somatic cell hybrid containing a single human X chromosome hearing the Xq27 fragile site was lethally irradiated and re-hybridized to its HPRT- Chinese hamster parent. One of 24 colonies surviving selection for HPRT was found to have retained human G6PD but not PGK. This line, X300-11 which shows Xq24-qter translocated to a hamster chromosome by trypsin G-banding and a single human chromatin fragment corresponding to this segment of the X by G-11 staining, expresse the fragile site on exposure to 5-fluorodeoxyuridine. Dot blots using total human DNA suggest that X3000-11 retains ∼0.2% of the human genome. By Southern blotting, X3000-11 retains Factor IX, DXS11 and DXS42 but lacks DXYS1, DXS3 and DXS17. This hybrid is being used to construct a cosmid library in the vector pCOS2 from which a sub-library of 500-1000 clones of human origin will be isolated using in vivo recombination with cloned Alu and Kpn family repeats. Such a sub-library will greatly facilitate chromosome walking to the fragile site as well as the testing fo individual clones for their ability ot create a folate-sensitive fragile by DNA transfer into permissive Chinese hamster recipient cells.