Biotinylation of Lambda DNA Concatemers

Double-stranded lambda phage DNA was purchased from Takara (Shiga, Japan). Concatemers of lambda DNA were prepared with T4 DNA ligase (Takara, Shiga, Japan) by incubating in ligation buffer for 1 h at 25°C. To biotinylate one end of the concatemeric DNA, a biotin-labeled oligonucleotide with the sequence 5′-GGGCGGCGACCT-biotin-3′ (Sigma-Aldrich), which is hybridized at the right cos site of lambda phage DNA, was added to the concatemeric DNA solution at a DNA:oligonucleotide ratio of 1:2 and incubated for 10 min at room temperature with T4 DNA ligase. After ligation of the biotin-labeled oligonucleotide, the concatemeric biotinylated DNA was isolated by 1% agarose gel electrophoresis in 1× TAE and extracted from gel slices by electro-elution.