Credit: © 2008 ACS

DNA polymerase — an enzyme that catalyses DNA replication — has been studied at subnanometre resolution with many state-of-the-art techniques. But no method has previously been reported for monitoring its base-by-base activity. Researchers from the Scripps Research Institute in California have now developed a nanopore device that can detect consecutive single-base extensions to a DNA primer catalysed by the enzyme.

Reza Ghadiri and colleagues1 threaded a single strand of DNA, with a polymer chain attached to one end, through an α-haemolysin protein pore. A small piece of complementary DNA — the primer — was added to the protruding end of the DNA strand. As new bases were added to the primer by the DNA polymerase, the molecular chain moved through the pore to accommodate the growing double-stranded region, which was too large to fit inside the narrow channel. When a potential is applied across an α-haemolysin pore, a current is produced, which is dependent on what molecules reside within the pore. With each base addition, the length of DNA within the pore decreased and a length of the polymer chain took its place, resulting in stepped increases in the current.

This new technique opens up possibilities for the study of biopolymers at a single-base resolution, and with further advances, could have applications in DNA sequencing.