Sample 1_p
All DNA oligonucleotides were obtained from Shanghai Sangon Biological Engineering Technology & Services Co., Ltd. (Shanghai, China). DNA sequence: ATCTC GACTA GTCAG N40 ATCCG AATGT CTCGG AT (N = A, T, G, C) (5' phosphate) The sample DNA was extracted by 10% denaturing polyacrylamide gel electrophoresis (dPAGE) or high-performance liquid chromatograph (HPLC). DNA molecules were concentrated by standard ethanol precipitation and purified by 10% dPAGE. The starting linear DNA library contains, in the 5' to 3' direction, a 5'-phosphate, a 5' 15-nt (nt: nucleotide) constant sequence element, a central 40-nt random region (N40), and a 3' 17-nt constant sequence element. The last sequence element is designed to a 6-base pair stem and a 5-nt loop, which positions the 3'-hydroxy terminus of the library in duplex form.