Title: Mechanism of DNA Sequence Alignment During Homologous Recombination

Speaker： Dr. Zi Qi

             Department of Biochemistry & Molecular Biophysics, Columbia University, New York, NY

Time： 1:00pm Nov 5th 2014

Address： Rm 102, East wing of Old Chemistry Building, Peking Unversity 

Chair：  Dr. Feng Liu,  Center for Quantitative Biology 

Abstract：

     Homologous recombination (HR) promotes the exchange genetic information between different DNA molecules. During HR, members of the RecA/Rad51 family of recombinases must align and pair ssDNA with a homologous dsDNA template, but the physical basis for these early stages of recombination remain largely undefined. Here we use single-molecule imaging to visualize Rad51 as it attempts to align and pair homologous DNA sequences in real-time. We show that Rad51 uses a length-based recognition mechanism while interrogating dsDNA, enabling robust kinetic selection of 8-nucleotide (nt) tracts of microhomology, which confines the search to sites with a high probability of being the homologous target. Successful pairing with a 9th nucleotide coincides with an additional reduction in binding free energy and subsequent strand invasion occurs in precise 3-nt steps, reflecting the unusual base triplet organization of the presynaptic complex. These findings provide crucial new insights into the physical and evolutionary underpinnings of DNA recombination.