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© The Rockefeller University Press, 0021-9525/2003/10/201 $8.00
The Journal of Cell Biology, Volume 163, Number 2, 201-201

The kinase knows

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 large noncatalytic portion of Hsl1 that binds to and inactivates the kinase domain. This autoinhibitory domain overlaps with three sites that bind to two different septin subunits. In vitro, septins activate the kinase by displacing the inhibitory domain. In vivo, the septins have to be polymerized, as previous results showed that unassembled subunits do not activate Hsl1. This may be due to the spacing of the septin binding sites and the need for all three sites to be filled to displace the inhibitory domain.

This sensing mechanim may extend to other cytoskeletal structures. Microtubules, for instance, are bound by a relative of Hsl1 called MARK. Says Snyder, "[the Hsl1 model] is attractive as a universal mechanism to monitor assembly of cytoskeletons specifically, and maybe macromolecular complexes in general."

Reference:

Hanrahan, J., et al. 2003. Mol. Cell. 12:663–673.[CrossRef][Medline]

Nicole LeBrasseur

lebrasn{at}rockefeller.edu

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This Article Full Text (PDF, 757K) PPT slides of all figures Alert me when this article is cited Services Email this article Similar articles in this journal Alert me to new content in the JCB Download to citation manager Citing Articles Citing Articles via CrossRef Citing Articles via Google Scholar Google Scholar Articles by LeBrasseur, N. Search for Related Content PubMed Articles by LeBrasseur, N. Social Bookmarking                            What's this?