Flicking the chromosome–attachment switch

Iain Cheeseman, Georjana Barnes (University of California, Berkeley, CA), and colleagues have peered into a 28-protein mix and found the individual residues responsible for attaching and detaching chromosomes and microtubules. The phosphorylation of these residues by Ipl1p (an Aurora kinase) apparently allows budding yeast cells to convert monopolar chromosome spindle attachments to bipolar attachments.

The group used the mass spectrometry (MS) expertise of Scott Anderson and John Yates (Scripps Research Institute, La Jolla, CA) to identify 28 yeast kinetochore proteins (including 5 previously unidentified proteins) in 4 subcomplexes. The same analysis identified 18 phosphorylation sites, 10 of which appear to be Ipl1p targets.

Mutation of individual sites for Ipl1p phosphorylation did not yield any phenotype. But mutation of four sites in the microtubule-binding Dam1p was...