Project Summary Mechanistic understanding of living things requires our understanding of how proteins and DNA interact together to generate functional chromosomes. This understanding is central to preserving human health, dealing with genetic disorders, and fighting pathogenic organisms. The proposed projects are focused on single-molecule analyses which permit direct visualization of biomolecule interactions, and can be used to analyze protein-DNA interactions in detail. The aims of the proposal include careful study of a facilitated dissociation "exchange" mechanism for removal of proteins from DNA that suggests a major revision of conventional descriptions of protein turnover on DNA, and which will affect a wide range of studies of gene regulatory and chromosome structural proteins. The second and third aims are focused on study of mechanisms of large "Structural Maintenance of Chromosomes" (SMC) protein complexes which mediate the folding of chromosomes in eukaryote cells. The second aim concerns understanding the mechanics of compaction and DNA substrate selection by the Smc5/6 complex, which plays a key role in separating replicated chromosomes from one another during cell division, while the third aim concerns direct microscopy observation of the mechanism by which Smc5/6 compacts DNA. The second and third aim will also include side-by-side comparisons of Smc5/6 and the more well-understood condensin complex. The highly mechanistic analyses of DNA processing machinery that are proposed will give us a stronger understanding of how cells interpret, fold and change their genomes, leading to a better understanding of pathologies where those functions are impaired, and better understanding of how to target those functions in pathogenic organisms.