Figure 1.

General strategy to form catenanes and knots. (Left) Sequence of events leading to the formation of catenanes. Three different oligonucleotides were used in each ligation reaction. The two pairing and ligation events are commutative, i.e. their relative order is not important for the final outcome (formation of catenanes). (Right) Sequence of events leading to formation of knots. Only one type of oligonucleotide is used in the ligation reaction. The sequence of pairing in the stem and loop region is crucial for the final outcome. Knots are only formed when stem is formed first. Unknotted circles are formed when the pairing in the loop precedes this in the stem.