The threats to the DNA in our cells are incredible. Radiation, carcinogens and even chemicals produced within the cell attack the DNA thousands of time every day. What is more incredible though is the cell’s DNA repair system, which you can read more about here and here. The worst kind of DNA damage is the so-called double-strand break where both strands of the double helix break. In response the cell mounts a swift and sophisticated response which new research is helping to elucidate.
One of the key proteins involved in this DNA repair, known as CtIP, has a 49 amino acid DNA-binding segment that has an important role in the repair job. Interestingly, this segment appears to be normally buried within the interior of CtIP. It is exposed when chemical signals indicating DNA damage modify the CtIP structure. The tool is now flipped open and ready to do its job.
Obviously this repair kit wouldn’t work without the CtIP protein. But it also wouldn’t work without the chemical signal that opens it up. Remove either one and the repair kit doesn’t work very well. Of course CtIP needs to have a binding site for the chemical signal, and CtIP needs to undergo just the right conformational change under the influence of the binding.
This is only the beginning of the repair kit’s complexity. There are several more important players in the choreography, without which the repair job would suffer. Nothing in biology makes sense in the light of evolution.