DNA Base Excision Repair (BER)

Michael Kubal, Computation Institute, University of Chicago

DNA bases can be damaged by oxidation, deamination, or akylation. The DNA repair process of BER consists of the following 5 steps.��

1) The lesion in the DNA caused by the damaged base is detected by a glycosylase that pinches the DNA. A damaged base forms an unstable bond with the base on the other strand of DNA. When the glycosylase pinches the DNA, the damaged base becomes exposed due to the unstable bond, and the glycosylase cleaves off the base leaving the deoxyribose phosphate moiety attached to the rest of the strand. Different glycosylases exist to detect different types of damage.

2) An endonuclease then breaks the single strand of DNA on the 5� side of the base- free deoxyribose moiety.

3) The deoxy ribose moiety is then excised by an exonuclease.

4) A DNA polymerase then fills in the gap with the correct base using the undamaged strand as a template.

5) A DNA ligase rejoins the phosphodiester backbone of the repaired strand.�

In some organism these five steps are performed by five separate proteins. In other organisms, some proteins are capable of performing multiple roles. This subsystem represents an on-going exploration of the types of damage each organism can detect, which organisms possess multi-functional roles, as well as the possibility of alternate roles for different conditions and/or redundancy.