The mechanism of homology search during double-strand break repair.
Martin Kupiec, Batia Liefshitz, Shira Goldstein, Adi Barzel
Mol. Micro & Biotechnology, Tel Aviv University, Ramat Aviv, Tel Aviv, 69978, Israel
Damage to DNA in the form of double-strand breaks (DSBs) arises as a consequence of ionizing radiation, mechanical stress, or from replication of single-stranded nicks. If repaired incorrectly, DSBs can cause genetic alterations or broken chromosomes, both of which are precursors to cancer. For these reasons, DSBs must be efficiently repaired to restore the integrity and functionality of the genome. In order to study the mechanism of DSB repair and its regulation, we have developed yeast strains in which a single DSB can be induced at will. A series of assays allow us to monitor the creation of the break, processing of the broken chromosomal ends, the homology search, pairing and invasion, which are then followed by DNA synthesis and re-ligation of the broken ends. Repair is highly efficient and synchronous. The role of various genes in DSB repair and regulation can be studied in this system. When a chromosome is broken, a genome-wide search for homologous sequences takes place. To date, very little is known about the mechanism that searches for homologous sequences. We will present results of experiments aimed at understanding the rules governing this search. These include competition experiments between donors of different sizes located at various points of the genome. The role of the resected ends in this process is also assessed.