The role of self-association in Fin1 function on the mitotic spindle.
Stabilization of spindle microtubules during anaphase is essential for proper chromosome segregation. Fin1 is a budding yeast protein that localizes to the poles and microtubules of the spindle during anaphase and contributes to spindle stability. The N-terminal half of Fin1 is phosphorylated at multiple sites by the cyclin-dependent kinase Clb5-Cdk1, and dephosphorylation in anaphase triggers its localization to the spindle. The C-terminal half of Fin1 contains coiled-coil motifs that are required for its self-association. Here we investigated the functional importance of the two regions of Fin1. Fin1 mutants lacking the C-terminal coiled-coil domains localized to spindle pole bodies but not along spindle microtubules. These mutants failed to self-associate and displayed reduced binding to microtubules in vitro but were functional in vivo and stabilized anaphase spindles when dephosphorylated. Deletion of the Fin1 C terminus suppressed the lethal phenotypes of the phospho-mutant Fin15A. Our findings suggest that the N-terminal region of Fin1 is sufficient for its regulated function as a spindle-stabilizing factor and that this function involves association with the spindle pole body. The ability of the C-terminal region to promote Fin1 self-association and microtubule binding may underlie the lethal effects of the deregulated Fin15A mutant.
Woodbury
Erika L
EL
Department of Physiology, University of California, San Francisco, California 94158-2517, USA.
Morgan
David O
DO
D000705:Anaphase; D003598:Cytoskeletal Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D009154:Mutation; D017434:Protein Structure, Tertiary; D012441:Saccharomyces cerevisiae / Q000737:chemistry / Q000166:cytology / Q000378:metabolism*; D029701:Saccharomyces cerevisiae Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D008941:Spindle Apparatus