Figure 1.

Schematic of DNA strand exchange mechanism for sequential addition of tiles. Rectangles represent the body of the tile, thin lines represent relevant DNA strands in the mechanism with an arrow indicating the 3’ end and a ladder showing base pairs between strands. Sequence segments of 5 nucleotides are labeled with lowercase letters, uppercase denotes 6-base sequences that are a one base augmentation of a 5-base sequence of the same letter, and complementary sequences are starred. a) A schematic representation of the five tiles tested in this paper. Augmented 6-base sequences are such that dB = Db, dF = Df, hF = Hf, and hJ = Hj. b) Binding is initiated at a 5-nucleotide toehold, c*, on the second tile (green). Strand exchange releases the tethered signal strand, allowing it to reach the 5-nucleotide toehold on the cover strand. c) The second strand exchange event removes the cover strand to release the sticky end, activating it. The activated 16-nucleotide glue retains only a 6-nucleotide sequence from the previous glue. On the next tile (two steps away from the initiator) the activated glue sequence will be completely independent of the initial glue sequence. d) Three-tile assembly after the addition of Tile C and the activation of its glue strand. e) Four-tile assembly. f) Schematic of the final assembly of five tiles. Note that in a complete assembly, all bases are paired except for the last output strand of 16 bases.