Adaptors are short double-stranded synthetic oligonucleotides that carry an internal restriction endonuclease recognition site and single-stranded tails at one or both ends. Adaptors are used to exchange restriction sites at the termini of linear DNA molecules. They may be purchased in phosphorylated and unphosphorylated forms. - [Read Attaching Adaptors to Protruding Termini Protocol]
This stage achieves four goals: polishing the ends of double-stranded DNA, ligation of synthetic linkers or adaptors, digestion of the attached linkers to create cohesive termini, and preparing the cDNA for cloning. - [Read Attachment of Linkers or Adaptors for Construction of cDNA Libraries]