Abstract
DNA double-strand breaks induced by ionizing radiation and chemotherapeutic agents activate damage response pathways initiated by ATM or ATR, resulting in the recruitment of DNA repair proteins at the damaged sites. Dynamics of RAD51, a central player at early stages of homologous recombination, in the nucleus have been well analyzed with being an excellent model in this field. Since homologous recombination consists of complex processes, it is regulated by a variety of proteins. However, dynamics of these proteins are only analyzed from the viewpoint of their association with RAD51. Identification of their dynamics in the nucleus contributes to exploration of the network of nuclear functions as well as a better understanding of their molecular functions. We have therefore examined the dynamics of DNA repair proteins that function in the proximity of RAD51 using human cells as models. It is well established that RAD52 plays a critical role in homologous recombination in yeasts, whereas its role in higher eukaryotes is unclear because its mutation does not exhibit drastic changes. When dynamics of RAD52 were examined using GFP-tagged RAD52, its focus formation reached the peak later than that of RAD51. Double immunofluorescence revealed that some foci colocalized with each other but others did not. These observations indicate that RAD51-independent role of RAD52, in addition to its RAD51-dependent role, is important in DNA repair. Such examination of dynamics in the nucleus proposes that DNA double-strand break repair may be more complicated than current models.
