Isolation of mouse x-chromosome specific DNA from an x-enriched lambda phage library derived from flow sorted chromosomes.

A lambda phage library enriched in X(7) chromosomal material has been constructed from flow sorted chromosomes isolated from mice carrying the Cattanach translocation T(X;7)1Ct. The flow sorted fraction that was cloned contained 40% X(7) chromosomes, so that the resulting lambda phage library should be more than 10-fold enriched for X chromosomal DNA. Approximately 100,000 lambda phage clones were obtained; of these, at least 80% were recombinant. Three quarters of recombinants were positive for mouse repetitive DNA as detected either by phage plaque filter hybridization or by Southern blotting. Recombinant DNA inserts were prepared from some of the remaining nonrepetitive phage fraction. The X-chromosome specificity of cloned DNA inserts was tested by hybridization to DNA from mouse-hamster somatic cell hybrids that had retained all or most of the mouse X as the only mouse chromosome and by comparison of the extent of hybridization to DNA from male and female mice. Out of nine cloned unique sequence segments successfully examined thus far, two were presumably derived from the X. Possession of phage library highly enriched for mouse X DNA should facilitate molecular studies of the control of X chromosome gene expression.