Host: The Japan Radiation Research Society
Non-chromatin nuclear domains are formed by proteins involved in nuclear functions such as transcription, replication and repair. During repair of DNA double-strand breaks (DSBs), a fraction of repair proteins form nuclear domains (Radiation Induced repari Foci, RIRF) at sites containing DSBs. RAD51, a eukaryotic RecA homologue, plays a central role in homologous recombinational repair of DSB in yeast and is conserved from yeast to human. RAD51 forms nuclear foci, and the percentage of cells containing RAD51 foci increase after induction of DNA damage. We have reported that RAD51 foci are formed specifically during S phase, and RAD51 proteins accumulate at sites containing DSBs in human cells.
To study the biological significance of RAD51 nuclear domains, we analyzed the changes of RAD51 nuclear domain components following ionizing irradiation using multicolor immunofluorescence technique. A fraction of RAD51 nuclear foci did not show collocalization with gammaH2AX, even after ionizing irradiation, suggesting the presence of DNA damage-independent RAD51 nuclear domains. Accumulation of ubiquitinated proteins were observed from immediately after induction of DNA damage. 53BP1, which interacts with a deubiquitination enzyme, was recruited to RAD51 nuclear domain in the late steps of DNA repair. These results suggest that RAD51 forms heterogenous nuclear domains after ionizing irradiation.
