Isolation of human chromosome 21-specific cosmids and their uses in mapping of cosmid contigs on chromosomal subregions

Summary A cosmid library of 3×10⁵ clones has been constructed from a human x hamster hybrid cell line, 153E9a3, which contains human chromosome 21 (HC21) as the only human chromosome. From 56,500 clones of this library, 229 HC21-specific cosmids have been isolated by their hybridization to total human DNA and by their failure to hybridize to total Chinese hamster DNA. The cosmids isolated were then characterized, of these, 28 cosmids (12.2% of those tested) containedNot1 site(s), and 41 cosmids were localized on the eight subregions of HC21 by differential hybridization withAlu-PCR products obtained from a hybrid mapping panel. The cosmids localized were further integrated into the existing contigs using the end-specific probes of the clone insert. Therefore, they provided useful anchor points for contig mapping and walking.