Figure 2.

Varying presentations of the tripeptide substrate to DNA in the open architecture. (A) Presentation with a short three-carbon tether linking the DNA anchor to the CXA tripeptide via a disulfide bond, illustrated with X = Tyr, i.e., CYA tripeptide. The initially random pool is N₄₀, and the loop on the right side is present only during the selection process. (B) Presentation with a longer hexa(ethylene glycol) (HEG) tether to the CYA tripeptide. (C) Presentation with untethered free CYA tripeptide and a DNA helper oligonucleotide in place of the DNA anchor. In all cases, the N-acetyl group on the amino terminus of the tripeptide was included to suppress potential amine nucleophilicity.