The goal of the research is to understand the mechanistic of human genetic recombination at the single molecular level.Homologous recombination, the exchange of sequences between homologous DNA molecules, is essential for accurate genome duplication, DNA damage repair and chromosome segregation. Single molecule analysis provides information on intermediate states, functional and structural variability and the distribution of variable states that cannot be recovered from bulk biochemical assays.Understanding the mechanism of DNA repair by homologous recombination requires detailed structural descriptions of recombination intermediates.We are uniquely poised to unravel key steps in homologous recombination at the molecular mechanistic level using state of the art imaging tools. We have a substantial track record in applying SFM topographic imaging to the understanding of DNA break repair mechanisms and other genome transactions. The recently developed method that combined SFM with single molecule sensitivity fluorescence will expand the information we can obtain from molecular imaging. In particular, our aims will be:1 Simultaneous localization of multiple human DNA repair factors acting on recombination intermediates.2 Analysis of DNA replication after repair.Homologous recombination proteins are the target for important treatment modalities against cancer. By analysing the mechanism through which these proteins cooperate in DSB repair, we expect to provide insights into their molecular assembly.Recombination proteins and DNA substrates labelled with flourophores will be used in single molecule microscopy assays. We have developed methods to combine SFM nm resolution topography and single molecule sensitivity fluorescence (Sanchez, et al., 2010). This SFM-fluorescence microscopy will be exploited here for specifically recognizing and localizing DNA repair factors.