Topography and ultrastructure of proteins involved in homologous recombination (HR) at cellular DNA damage sites with dSTORM nanoscopy. Upon DNA double strand break (DSB) generated by ionizing (X-ray) radiation, RAD51 recombinase assembles at resected single stranded (ss) DNA into helical nanofilaments of several hundrets nanometers in length. Prior to this, a DNA break is detected by NMR complex, resected and prepared for RAD51 filament assembly, by the succesive action of various proteins, among others RPA (Replication Protein A), also involvd in DNA replication. RPA guides the end-resection of dsDNA by nucleases and covers a newly created ssDNA tracks to protect it from an enzymatic cleavage. BRCA2 is a tumor suppresor, whose mutations are associated with multiple familial tumors. BRCA2 mediates HR by targetting RAD51 to a DNA damage sites. BRAC2 promotes a replacement of RPA with RAD51 molecules to form an extended RAD51 filament. The RAD51 nucleofilament catalizes homologous pairing and strand exchange with homologous dsDNA to exacute HR. How the RAD51 filament performs a homology search in a templeate homologue DNA is still unclear. Using super-resolution imaging of DNA damage foci we showed, that end-resection (marked by RPA) and RAD51 filament assembly occurs concurently and not succesively as it was previously thought. WE also showed, that BRC repeats region of BRCA2 is essential to target RAD51 molecules to DNA damage sites, and the C-terminus domain of BRCA2, is essential to form an extended RAD51 filament. Read more