Patrick Sung DPhil, Ph.D.
Professor of Molecular Biophysics and Biochemistry and of Therapeutic Radiology
Repair of DNA double-strand breaks; Repair by homologous recombination; Repair by DNA end-joining
Endogenous free radicals and environmental agents such as ionizing radiation induce DNA double-strand breaks. The repair of these breaks is crucial for the maintenance of genome stability. Two distinct pathways help eliminate DNA double-strand breaks. In homologous recombination, the repair of a broken DNA molecule requires an intact homologous duplex to direct the process. Alternatively, a pathway known as non-homologous DNA end joining (NHEJ) simply rejoins the ends of the broken DNA molecule. Our research efforts focus on delineating the mechanisms of these two DNA repair pathway.
Repair by homologous recombination
The recombinational repair of DNA double-strand breaks is mediated by a group of genes called the RAD52 epistasis group. In mammals, the efficiency of recombinational DNA repair is modulated by the tumour suppressors BRCA1 and BRCA2, providing compelling evidence that this repair pathway functions to suppress cancer formation. Importantly, recombinational DNA repair is also required for the removal of interstrand DNA crosslinks induced by bifunctional crosslinking agents, which are commonly used to treat various malignancies. In 1994, we identified the yeast Rad51 protein, a key member of the RAD52 group, as the recombinase that mediates the “homologous DNA pairing and strand exchange “reaction central to all recombination-dependent processes, including the repair of DNA double-strand breaks. This finding marked the beginning of studies on recombination enzymology in eukaryotic organisms and has created a much-needed experimental framework for dissecting the role of the other RAD52 group members in the recombination reaction.