Partial purification and characterization of DNA from the human X chromosome

Human X chromosome DNA was partially purified from a mouse-human hybrid cell line containing a single human chromosome, the X. Enrichment of such DNA was accomplished by two sequential reassociations of radiolabeled hybrid cell DNA with large excesses of mouse DNA. Unreassociated hybrid cell DNA was used as a probe for human X chromosome sequences. The human-specific fraction of probe DNA contained three components. Two of these reassociated to human DNAs at rates proportional to the number of X chromosomes present. These two components were thus localized to the X chromosome. One of these X-specific components, representing about 80% of human-specific probe DNA, consisted of single copy or very low order reiterated DNA. The second X-specific component, representing about 10% of human-specific probe DNA, was about 20-30 times more reiterated. The remaining 10% of human-specific probe DNA, although derived from the X chromosome, reassociated to human DNAs at a rate independent of the number of X chromosomes present. This component was thus homologous to autosomal as well as X chromosome DNA. The probe DNA accounts for approximately half of the human X chromosome, suggesting that the remainder may have homology with mouse DNA.