Investigation of chromosome dynamics in bacteria

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In contrast to eukaryotic cells that contain a mitotic machinery to separate chromosomes it is unclear how prokaryotes segregate their DNA into future daughter cells. Key players in chromosome condensation and segregation are SMC proteins. We have shown that likewise to eukaryotic cells SMC is essential for chromosome segregation in B. subtilis. We have identified two proteins, ScpA and ScpB that are conserved in prokaryotes and that form a ternary complex with SMC. Fluorescence microscopy has shown that the SMC complex localizes in a dynamic cell cycle dependent manner and is mostly present within specific sites close to the cell poles. Additional data suggest that from these sites the SMC complex actively pulls the sister chromosomes towards opposite cell poles. We have purified all 3 proteins and distinct parts of SMC and have shown that ScpA and ScpB bind to the SMC head domains, while SMC embraces DNA as a ring-like structure, which presents a novel DNA condensation mechanism that needs to be further elucidated. We have also found that several proteins required for repair of DNA double strand breaks are dynamically and transiently recruited to specific sites on the DNA after damage induction but in a differential fashion. Further analysis will provide detailed insight in their function and interdependence.