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Published online
doi:10.1083/jcb.200905114
The Journal of Cell Biology, Vol. 187, No. 4, 497-511
The Rockefeller University Press, 0021-9525 $30.00
© Geymonat et al.
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Article

Lte1 contributes to Bfa1 localization rather than stimulating nucleotide exchange by Tem1



Marco Geymonat, Adonis Spanos, Geoffroy de Bettignies, and Steven G. Sedgwick

Division of Stem Cell Biology and Developmental Genetics, National Institute for Medical Research, London NW7 1AA, England, UK

Correspondence to Marco Geymonat: gmarco{at}nimr.mrc.ac.uk

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.

Abbreviations used in this paper: dSPB, daughter-directed SPB; FEAR, Cdc14 early anaphase release; GAP, GTPase-activating protein; GEF, guanosine nucleotide exchange factor; HyA, hyperactive; MBP, maltose-binding protein; MEN, mitotic exit network; mSPB, maternal SPB; SIN, septation initiation network; SPB, spindle pole body; SPoC, spindle position checkpoint; YEP, yeast extract peptone.

© 2009 Geymonat et al.
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