Bir1 is required for the tension checkpoint.
The Saccharomyces cerevisiae chromosomal passenger proteins Ipl1 (Aurora B) and Sli15 (INCENP) are required for the tension checkpoint, but the role of the third passenger, Bir1, is controversial. We have isolated a temperature-sensitive mutant (bir1-107) in the essential C-terminal region of Bir1 known to be required for binding to Sli15. This allele reveals a checkpoint function for Bir1. The mutant displays a biorientation defect, a defective checkpoint response to lack of tension, and an inability to detach mutant kinetochores. Ipl1 localizes to aberrant foci when Bir1 localization is disrupted in the bir1-107 mutant. Thus, one checkpoint role of Bir1 is to properly localize Ipl1 and allow detachment of kinetochores. Quantitative analysis indicates that the chromosomal passengers colocalize with kinetochores in G1 but localize between kinetochores that are under tension. Bir1 localization to kinetochores is maintained in an mcd1-1 mutant in the absence of tension. Our results suggest that the establishment of tension removes Ipl1, Bir1, and Sli15, and their kinetochore detachment activity, from the vicinity of kinetochores and allows cells to proceed through the tension checkpoint.
Shimogawa
Michelle M
MM
Department of Biochemistry, University of Washington, Seattle, WA 98195-7350, USA.
Widlund
Per O
PO
Riffle
Michael
M
Ess
Michael
M
Davis
Trisha N
TN
D000483:Alleles; D064127:Aurora Kinases; D002453:Cell Cycle; D016764:Cell Polarity; D015825:Chromosomes, Fungal / Q000378:metabolism; D005656:Fungal Proteins / Q000737:chemistry / Q000378:metabolism*; D047908:Intracellular Signaling Peptides and Proteins; D018386:Kinetochores / Q000378:metabolism; D008677:Metaphase; D009154:Mutation / Q000235:genetics; D011494:Protein Kinases / Q000378:metabolism; D017346:Protein Serine-Threonine Kinases; D021381:Protein Transport; D012441:Saccharomyces cerevisiae / Q000166:cytology* / Q000378:metabolism*; D029701:Saccharomyces cerevisiae Proteins / Q000378:metabolism; D013696:Temperature
D005656:Fungal Proteins; D047908:Intracellular Signaling Peptides and Proteins; D029701:Saccharomyces cerevisiae Proteins; D011494:Protein Kinases; D064127:Aurora Kinases; C576961:IPL1 protein, S cerevisiae; D017346:Protein Serine-Threonine Kinases