Hung-Wen Li 's Laboratory

Genomic DNA is maintained with high fidelity to guarantee the integrity of genetic information. Damaged DNA must be properly repaired by sophisticated DNA repair systems to sustain cell viability and genomic stability. Homologous recombination is the major pathway for repairing DNA double strand breaks and for re-initiating stalled replication forks in E. coli and eukaryotes. In E. coli, there are several important proteins involved in homologous recombination: RecA protein is essential for pairing homologous DNA, and for promoting the strand exchange process. RecBCD protein is a DNA helicase/nuclease that processes damaged DNA ends and generates ssDNA. RecQ protein is a DNA helicase that is involved in several stages in RecF-mediated homologous recombination.

Homologous recombination has been thought to be the potential pathway for targeting gene delivery. Defects in human helicase family genes have implications in cancer and aging process. Human Rad51, the structural and functional homolog of RecA, has been found to directly interact with breast cancer genes. We are interested in understanding the molecular mechanisms of the proteins involved in this pathway through the combination of the conventional biochemistry study and the single-molecule biophysics approaches.

Proposed function of RecBCD and RecA in homologous recombination in E. coli (figure from Kowaczykowski, 2000). RecBCD enzyme binds to a blunt-end DNA from a double-stranded DNA break. It unwinds the dsDNA and prefereintially degrades the 3’-terminating strand (top strand). Interaction with χ results in attenuation of the 3’ → 5’ nuclease activity, the activation of a weaker 5’ → 3’ nuclease activity, and the facilitated loading of RecA protein onto the χ-containing ssDNA. The resulting RecA/ssDNA filament can then invade homologous dsDNA.
　