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Overview of my studies

My primary research focuses on the molecular mechanisms of DNA homologous recombination in eukaryotes, using yeast as a model organism. Homologous recombination is the major pathway of accurate DNA double-strand break (DSB) repair in cells, making it extremely important for cell survival. Because homologous recombination does not introduce mutations into the genome, it is crucial for maintaining genome integrity, preventing disease, and reproduction.

Basic scheme of DSB repair by recombination
Fig. 3. Basic scheme of DSB repair by recombination. First, broken DNA is processed to produce single-stranded tails. Then one tail invades to pair with the homologous DNA (red). The lost DNA information is copied from the homologous DNA template by DNA polymerase. Two DNA molecules are then resolved (only one of four possible resolutions are drawn).
Fig. 3 is the model for homologous recombination as it was understood in 1995 when I began my investigation into the mechanisms of DNA recombination. The overall scheme shown in Fig. 3 is still used, but with greater detail at each step. I will describe my contributions to the current model starting from Fig. 3.

As shown in Fig. 3, homologous DNA recombination is composed of multiple steps that alter the structure of DNA (step 1 to 4). My early research on homologous recombination began with the detailed biochemical analysis of step 2, DNA strand invasion. More recently my research has expanded into investigation of the biochemical mechanisms involved in step 3, DNA synthesis and the second-end capture. My first project, investigating the contribution of the proteins Rad51 and RPA (Replication Protein-A) to strand invasion started in 1995, when I joined Professor Stephen C. Kowalczykowski's laboratory at the University of California, Davis, as a post-doctoral fellow. This first study was then extended to the characterization of Rad52. My research method was biochemical analyses of the purified proteins using model DNA substrates that mimicked homologous recombination. When I found the protein activity that is meaningful for recombination, I updated the working models of molecular mechanism of homologous recombination. I was given extraordinary research freedom in Professor Kowalczykowski's laboratory, conducting most of my work there independently as well as mentoring four graduate and several undergraduate students. At Ohio University, I have continued investigating the biochemistry of step 2 and have begun to shift my research focus to step 3 (see Fig. 3). My research at Ohio University has been done with a post-doc, Dr. Noriko Kantake (2004-2007), and recently by two graduate students, Jian Li and Nilesh Khade (joined us in 2009).