[Analysis of human chromosome 21q: isolation of linking clones and generation of STSs, and construction of P1 phage library].

To clarify the structure of human chromosome 21q, we isolated many Sequence-Tagged NotI and SfiI linking clones. For further analysis, we constructed a P1 phage library specific for this chromosome. The library presently consists of 1516 clones, amounting to 2 equivalents of this chromosome. For rapid clone identification, we constructed a 3-dimensional library containing DNA from P1 clones, and a PCR-based screening approach was used to isolate 38 positives from 50 sequence-tagged sites specific for this chromosome. And also by this PCR-based chromosome walking procedure using STSs from sequences from insert-end of P1 clones, we constructed a contig spanning the entirety of the human beta-amyloid precursor protein gene consisted of eight P1 clones and a contig consisted of nine P1 clones on D21S8 region.