TOPO cloning

TOPO cloning is a molecular biology technique in which blunt-ended DNA fragments amplified by PCR are cloned into specific vectors without the requirement for DNA ligases. This technique utilizes the inherent biological activity of DNA topoisomerase I, which cleave and rejoin DNA ends at the 3' phosphate group. A schematic view of the technique can be observed in the image below.

Figure 1. TOPO cloning overview

It has many applications in molecular biology. For instance, in the ChIP-exo technique, it's the first step to verify the cDNA library that will be sequenced afterwards.