The mitotic checkpoint gene BubR1 has two distinct functions in mitosis.
BubR1 is one of two putative vertebrate homologs of the yeast spindle checkpoint protein Bub1. We have used deletion and point mutants to elucidate the functions of BubR1 in mitosis. The nocodazole-activated spindle checkpoint of HeLa cells was disrupted by expression of a 39 amino acid fragment (residues 382-420) of BubR1 containing the Bub3-binding GLEBS motif. In contrast, we observed normal checkpoint function in a truncation mutant comprising residues 1-477, despite the lack of the C-terminal BubR1 kinase domain. In the absence of nocodazole, expression of the 477 amino acid fragment slowed progress through prometaphase of mitosis, causing accumulation of mitotic cells. This accumulation was also seen in a kinase dead mutant. The prolongation of mitosis required both kinetochore binding and an intact, functional spindle checkpoint. The prolongation of mitosis by kinase deficient BubR1 constructs indicates a crucial role for the BubR1 C-terminal kinase domain in chromosome movement, in addition to the role of the N-terminus in the checkpoint.
Harris
Loleta
L
Department of Virology and Molecular Biology, St. Jude Children's Research Hospital, 332 North Lauderdale Street, Memphis, TN 38105-2794, USA.
Davenport
James
J
Neale
Geoffrey
G
Goorha
Rakesh
R
D018797:Cell Cycle Proteins / Q000235:genetics* / Q000378:metabolism / Q000502:physiology*; D017353:Gene Deletion; D005786:Gene Expression Regulation / Q000235:genetics / Q000502:physiology; D006367:HeLa Cells; D006801:Humans; D008938:Mitosis / Q000235:genetics / Q000502:physiology*; D010770:Phosphotransferases / Q000172:deficiency / Q000502:physiology; D017354:Point Mutation; D011494:Protein Kinases / Q000235:genetics* / Q000502:physiology*; D017346:Protein Serine-Threonine Kinases
D018797:Cell Cycle Proteins; D010770:Phosphotransferases; D011494:Protein Kinases; C584277:BUB1 protein, human; C090464:Bub1 spindle checkpoint protein; D017346:Protein Serine-Threonine Kinases