Condensins are large protein complexes whose name reflects their roles in establishing and maintaining chromosome condensation during cell cycle progression. Vertebrates contain two such complexes, condensin I and condensin II, both of which are essential for establishing mitotic chromosome architecture and for mediating chromosome segregation. Their individual cellular roles have, however, remained somewhat of a mystery. To elucidate these functions, Damien Hudson and co-workers (p. 1591) establish conditional knockouts of essential components of condensin I (CAP-H) and condensin II (CAP-D3) in chicken DT40 cells. Using this set-up, they show that both condensin complexes are essential for cell division and survival. During anaphase, cells that lack functional condensin II display a large number of anaphase bridges; cells without condensin I, however, form finer chromatin threads. In addition, the absence of condensin I results in shorter and wider chromosomes during metaphase, but loss of condensin II results in the formation of long, stretched chromosomes that are twisted and bent. On the basis of these observations, the authors propose that condensin II mediates long-range DNA interactions that provide axial rigidity, whereas condensin I uses this initial structure to wrap DNA into compact chromatin loops.
- © 2012.