Geymonat Marco, Spanos Adonis, de Bettignies Geoffroy, Sedgwick Steven G
Division of Stem Cell Biology and Developmental Genetics, National Institute for Medical Research, London NW7 1AA, England, UK.
J Cell Biol. 2009 Nov 16;187(4):497-511. doi: 10.1083/jcb.200905114.
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.
Lte1是一种有丝分裂调节因子，长期以来被认为是Tem1的鸟苷核苷酸交换因子（GEF），Tem1是一种小的鸟苷三磷酸酶，控制酿酒酵母有丝分裂退出网络的活性。我们证明这个模型需要重新评估。在体外未检测到GEF活性，对Lte1假定的GEF结构域的突变分析表明，Lte1的活性依赖于与Ras的相互作用以定位在芽皮层，而不是提供核苷酸交换。相反，我们发现Lte1可以决定Bfa1在纺锤体极体（SPB）的亚细胞定位。在Lte1必不可少的条件下，Lte1促进了母本SPB上Bfa1的丢失。此外，在纺锤体未对齐的细胞中，Lte1在母细胞中的错误定位促进了Bfa1从一个SPB的丢失，并允许绕过纺锤体位置检查点。我们观察到lte1突变体表现出极性帽的异常定位，极性帽是肌动蛋白细胞骨架的组织者。我们提出，Lte1在细胞极化中的作用是其对有丝分裂调节做出贡献的基础。
