Tightening the Belt on Polymerases: Evaluating the Physical Constraints on Enzyme Substrate Size.

To test the limits of polymerase enzyme activity on geometrically constrained DNAs, four very small synthetic circular DNAs were constructed by using newly developed methods. Surprisingly, even a 13-nucleotide circular DNA (1) can be copied successfully by both DNA and RNA polymerases, despite the very small diameter and large degree of distortion in this synthetic DNA. The picture shows models to indicate the relative sizes of 1 and the Klenow fragment of the DNA polymerase I from E. coli.