ChIP-exo definition

Chromatin immunoprecipitation with exonuclease treatment (ChIP-exo) is a type of chromatin immunoprecipitation developed by researchers in order to increase the mapping resolution of the target DNA sequence where a protein binds, such as transcription factors.

The exonucleases are added after the antibody-coupled chromatin is precipitated in order to cleave the double-stranded DNA from the 5' ends until the bound protein, where they stop. In ChIP-exo two different exonucleases are used: Lambda exonuclease, which cleaves the DNA, and RecJ exonuclease, which eliminates single-strand background DNA.

Figure 1. Secondary structure of lambda (left) and RecJ (right) exonucleases. Lambda exonuclease presents one color per each subunit, and a small DNA molecule (in purple) to show where the reaction takes place.