Genetic studies on the interaction between base excision repair and recombinational repair using human gene knockout cells

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In this study, we have performed genetic analysis on the interaction between base excision repair and recombinational repair in human cells. Specifically, we disrupted, by means of gene targeting using Nalm-6 cells, the PolB, Rad54, and Lig4 genes involved in base excision repair homologous recombination, or nonhomologous end-joining, respectively. Additionally, we tried to make double-knockout mutant cell lines for those genes. We investigated the growth rate, cell cycle distributions, and recombination capacity of these mutants. Furthermore, using these mutants, we have successfully analyzed cellular sensitivity to a variety of genotoxic agents such as X-rays, UV light, alkylating agents, hydrogen peroxide, topoisomerase inhibitors, and replication stress. These studies led us to conclude that homologous recombination is important for repairing DNA double-strand breaks that arose from single-strand breaks. Most importantly, this work has highlighted the genetic interaction between DNApolymerase beta and DNAligase W in human cells.