DNA dA tailing in ChIP-exo

The term dA tailing refers to the addition of deoxyadenosine monophosphate (dAMP) nucleotides to the 3' ends of DNA strands. This reaction is carried out by the exo- Klenow fragment of DNA polymerase, which lacks 3'-->5' exonuclease activity.

In the ChIP-exo technique, these tails will be attached before adding the adapters, which means that will be used in two different steps of the technique:

• While performing on-bead modifications. Specifically, to the blunt-ended DNA from the antibody coupled protein-DNA complexes.

• While performing off-beads modifications. Once the DNA has been treated with exonucleases and it has been purified after detaching from proteins, a new dA tailing must be performed to add the second adapters.