ISOLATION OF HUMAN-CHROMOSOME 21-SPECIFIC COSMIDS AND THEIR USES IN MAPPING OF COSMID CONTIGS ON CHROMOSOMAL SUBREGIONS

A cosmid library of 3x10(5) 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 libra ry, 229 HC21-specific cosmids have been isolated by their hybridizatio n to total human DNA and by their failure to hybridize to total Chines e hamster DNA. The cosmids isolated were then characterized, of these, 28 cosmids (12.2% of those tested) contained Notl site(s), and 41 cos mids were localized on the eight subregions of KC21 by differential hy bridization with Alu-PCR products obtained from a hybrid mapping panel . The cosmids localized were further integrated into the existing cont igs using the end-specific probes of the clone insert. Therefore, they provided useful anchor points for contig mapping and walking.