Lte1 contributes to Bfa1 localization rather than stimulating nucleotide exchange by Tem1.
Lte1 is a mitotic regulator long envisaged as a guanosine nucleotide exchange factor (GEF) for Tem1, the small guanosine triphosphatase governing activity of the Saccharomyces cerevisiae mitotic exit network. We demonstrate that this model requires reevaluation. No GEF activity was detectable in vitro, and mutational analysis of Lte1's putative GEF domain indicated that Lte1 activity relies on interaction with Ras for localization at the bud cortex rather than providing nucleotide exchange. Instead, we found that Lte1 can determine the subcellular localization of Bfa1 at spindle pole bodies (SPBs). Under conditions in which Lte1 is essential, Lte1 promoted the loss of Bfa1 from the maternal SPB. Moreover, in cells with a misaligned spindle, mislocalization of Lte1 in the mother cell promoted loss of Bfa1 from one SPB and allowed bypass of the spindle position checkpoint. We observed that lte1 mutants display aberrant localization of the polarity cap, which is the organizer of the actin cytoskeleton. We propose that Lte1's role in cell polarization underlies its contribution to mitotic regulation.
Geymonat
Marco
M
Division of Stem Cell Biology and Developmental Genetics, National Institute for Medical Research, London NW7 1AA, England, UK. gmarco@nimr.mrc.ac.uk
Spanos
Adonis
A
de Bettignies
Geoffroy
G
Sedgwick
Steven G
SG
D002453:Cell Cycle / Q000235:genetics; D016764:Cell Polarity / Q000235:genetics; D003598:Cytoskeletal Proteins / Q000235:genetics / Q000378:metabolism*; D020662:Guanine Nucleotide Exchange Factors / Q000235:genetics / Q000378:metabolism* / Q000502:physiology; D042541:Intracellular Space / Q000235:genetics / Q000378:metabolism; D008938:Mitosis / Q000235:genetics; D020559:Monomeric GTP-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D017354:Point Mutation; D029701:Saccharomyces cerevisiae Proteins / Q000235:genetics / Q000378:metabolism* / Q000502:physiology*; D012689:Sequence Homology, Nucleic Acid; D008941:Spindle Apparatus / Q000235:genetics / Q000378:metabolism
C119117:BFA1 protein, S cerevisiae; D003598:Cytoskeletal Proteins; D020662:Guanine Nucleotide Exchange Factors; C089357:LTE1 protein, S cerevisiae; D029701:Saccharomyces cerevisiae Proteins; C089965:TEM1 protein, S cerevisiae; D020559:Monomeric GTP-Binding Proteins