This hypothesis is supported by the observation that replacing the wild-type mukB allele in E. This hyper-condensation of the DNA required the MukB-Topo IV interaction, but not the catalytic activity of Topo IV, suggesting that the combination of Topo IV and MukB might be serving as a scaffold for DNA compaction. The addition of Topo IV to these MukB DNA condensation assays resulted in increased DNA condensation. ![]() We showed using two different assays that this latter model was not operative for MukB. 6) for MukB-mediated DNA condensation that was distinct from the prevailing view arguing that SMC proteins condense DNA by topologically trapping the DNA in the tripartite complex formed by the SMC protein and its accessory proteins. We demonstrated that loop stabilization was the result of hinge-hinge interactions between MukB dimers. We showed that the faster-moving complex was a result of MukB stabilizing negative supercoils in the topologically unconstrained plasmid and that the slower-moving protein-DNA complex was a result of MukB stabilizing large relaxed loops in the DNA. Higher concentrations of MukB caused the plasmid-DNA complex to move more slowly than the DNA alone, as expected. In these assays, a large nicked DNA plasmid when bound by MukB migrated faster in the gel than the plasmid alone. We developed gel electrophoresis-based assays that could be used to easily score DNA condensation. 5), interacted physically and that this interaction stimulated the activity of Topo IV. ![]() Our interest in these processes stems in large part from our observation that the major cellular chromosomal decatenase, Topoisomerase IV, and the cellular condensin, MukB (Fig. Management of chromosome shape and topology in bacteria falls to three groups of proteins: the DNA topoisomerases, the structural maintenance of chromosome proteins (SMC), and the small double-strand DNA-binding nucleoid-associated proteins. Chromosome compaction is on the order of several thousand fold, yet these chromosomes have to be unraveled every cell cycle to be replicated accurately and the daughter chromosomes must be topologically unlinked to allow their separation and segregation into the daughter cells. Our chromosomes are much longer than the space in which they are packaged in the cell.
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