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Transgenic mice containing a 248-kb yeast artificial chromosome carrying the human beta-globin locus display proper developmental control of human globin genes.

Transgenic mice were generated using a purified 248-kb yeast artificial chromosome (YAC) bearing an intact 82-kb human beta-globin locus and 148 kb of flanking sequence. Seventeen of 148 F0 pups were transgenic. RNase protection analysis of RNA isolated from the blood of 13 gamma- and beta-globin-positive founders showed that only the human beta-globin gene was expressed in the adult founders. Studies of F1 and F2 fetuses demonstrated that the genes of the beta-locus YAC displayed the proper developmental switches in beta-like globin gene expression. Expression of epsilon- and gamma-globin, but not beta-globin, was observed in the yolk sac, there was only minor gamma and mostly beta expression in the 14-day liver, and only beta mRNA in the blood of the adult animals. Structural data showed that the locus was intact. These results indicate that it is now possible to dissect regulatory mechanisms within the context of an entire locus in vivo by using the ability to perform mutagenesis efficiently in yeast via homologous recombination, followed by purification of the altered YAC and its introduction into mice.