Hsl1 (red), is activated at the bud neck by septin binding.

Snyder/Elsevier

CFells monitor the assembly of cytoskeletal structures via direct binding and activation of a checkpoint kinase, as shown by Jessie Hanrahan and Michael Snyder (Yale University, New Haven, CT).

Cytoskeletal reorganization is needed during various events in the cell cycle. In budding yeast, for example, a ring of septin filaments separates the mother cell from the forming bud. The ring must be completed before the cell can enter mitosis. This landmark is signaled by the Hsl1 kinase, which is activated upon ring assembly. Snyder wondered, “how do [cells] recognize when a macromolecular complex like the cytoskeleton is assembled? The thought seems daunting at first.” But he found a relatively simple answer for Hsl1—it is either bound to the septin ring or is in an inactive conformation.

The authors identified a site in the...

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