Probing the mechanisms that couple genome segregation to chromosome organisation in Archaea

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Chromosome segregation is a fundamental process in all life forms. It requires the concerted action of dedicated proteins and coordination with cellular transactions, such as DNA organization, replication and cell division. The mechanisms that mediate this cell-cycle event in eukaryotes and bacteria are well established. In contrast, chromosome segregation is poorly defined in archaea, the third domain of life.

We have investigated a hybrid machine consisting of two interacting proteins, SegA and SegB, that play a key role in archaeal chromosome segregation. SegA is an orthologue of bacterial Walker ParA proteins. SegB is an archaea-specific DNA-binding factor that recognizes palindromic DNA motifs. Our ChIP-seq studies have revealed multiple SegB binding motifs scattered across the chromosome. Consistent with these results, microscopy has shown that SegB forms multiple foci on the chromosome, which then coalesce into large patches. Moreover, atomic force microscopy studies have shown that SegB bridges distant DNA sites, forming loop structures. These unpublished findings support the hypothesis that SegB might mediate chromosome organization prior to and in preparation for segregation. Moreover, recently we have solved the structures of SegA, SegB and respective DNA complexes, which provide snapshots into the mechanism of action of the proteins.

The overarching aim of the project is to establish the mechanisms through which the SegAB complex mediates genome segregation and how this process is coupled to chromosome organization. Cross-disciplinary approaches ranging from chromosome conformation capture and structured illumination microscopy to cross-linking mass spectrometry and cryo electron microscopy will provide transformative, multifaceted insights into the mechanism of action of the SegAB complex. The studies will open new perspectives on chromosome biology that will broaden mechanisms and principles established for the other two domains of life.