CONSTRUCTION OF A DNA-TRUNCATED OCTAHEDRON

A covalently closed molecular complex whose double-helical edges have the connectivity of a truncated octahedron has been assembled from DNA on a solid support. This three-connected Archimedean solid contains six squares and eight hexagons, formed from 36 edges arranged about 24 vertices. The vertices are the branch points of four-arm DNA junctions, so each vertex has an extra exocyclic arm associated with it. The construct contains six single-stranded cyclic DNA molecules that form the squares and the extra arms; in addition, there are eight cyclic strands that correspond to the eight hexagons. The molecule contains 1440 nucleotides in the edges and 1110 in the extra arms; the estimated molecular weight for the 2550 nucleotides in the construct is 790 kDa. Each edge contains two turns of double-helical DNA, so that the 14 strands form a catenated structure in which each strand is linked twice to its neighbors along each edge. Synthesis is proved by demonstrating the presence of each square in the object and then by confirming that the squares are flanked by tetracatenane substructures, corresponding to the hexagons. The success of this synthesis indicates that this technology has reached the stage where the control of topology is in hand, in the sense of both helix axis connectivity and strand linkage.