Figure 16. Synthesis of Four Topologies from a Single Strand of DNA.

X and X' represent a turn of DNA and its complement, as do Y and Y'. Both have a Z-forming propensity, but that of Y-Y' is higher. As the Z-forming nature of the solution increase, the main ligation product changes from a circle (very low ionic strength), to a trefoil knot with negative nodes (both turns B-DNA), to a figure-8 knot (the Y turn is Z-DNA), to a trefoil knot with positive nodes (both turns are Z-DNA).