• circulating DNA;
  • short cell-surface-bound DNA;
  • human endothelial cells;
  • ligation of single-stranded DNA

To isolate the DNA fragments bound to cell-surface proteins with high affinity, peptide–DNA complexes were obtained by mild treatment of human endothelial cells with trypsin. After binding of nucleoprotein complexes to BrCN-Sepharose and extensive washing, 7–11 nt DNA fragments were eluted with acidic buffer, labeled with 32P, and isolated by PAGE. The fragments were ligated to double-stranded oligonucleotide adapters, amplified by PCR, and cloned in pBluescript II KS (+) vector. Sequences of 12 clones containing the insert of cell-surface-bound 7–11-mer DNA fragments were obtained.