Stegmeier Frank, Huang Julie, Rahal Rami, Zmolik Jessica, Moazed Danesh, Amon Angelika
Center for Cancer Research, Howard Hughes Medical Institute, Massachusetts Institute of Technology, E17-233, 40 Ames St., Cambridge, MA 02139, USA.
Curr Biol. 2004 Mar 23;14(6):467-80. doi: 10.1016/j.cub.2004.03.009.
The protein phosphatase Cdc14 is a key regulator of exit from mitosis in budding yeast. Its activation during anaphase is characterized by dissociation from its inhibitor Cfi1/Net1 in the nucleolus and is controlled by two regulatory networks. The Cdc14 early anaphase release (FEAR) network promotes activation of the phosphatase during early anaphase, whereas the mitotic exit network (MEN) activates Cdc14 during late stages of anaphase.
Here we investigate how the FEAR network component Spo12 regulates Cdc14 activation. We identify the replication fork block protein Fob1 as a Spo12-interacting factor. Inactivation of FOB1 leads to premature release of Cdc14 from the nucleolus in metaphase-arrested cells. Conversely, high levels of FOB1 delay the release of Cdc14 from the nucleolus. Fob1 associates with Cfi1/Net1, and consistent with this observation, we find that the bulk of Cdc14 localizes to the Fob1 binding region within the rDNA repeats. Finally, we show that Spo12 phosphorylation is cell cycle regulated and affects its binding to Fob1.
Fob1 functions as a negative regulator of the FEAR network. We propose that Fob1 helps to prevent the dissociation of Cdc14 from Cfi1/Net1 prior to anaphase and that Spo12 activation during early anaphase promotes the release of Cdc14 from its inhibitor by antagonizing Fob1 function.
蛋白磷酸酶Cdc14是芽殖酵母有丝分裂退出过程中的关键调节因子。其在后期的激活表现为在核仁中与其抑制剂Cfi1/Net1解离，并受两个调节网络控制。Cdc14早期后期释放（FEAR）网络促进后期早期磷酸酶的激活，而有丝分裂退出网络（MEN）在后期后期激活Cdc14。
在此我们研究FEAR网络组件Spo12如何调节Cdc14的激活。我们鉴定出复制叉阻滞蛋白Fob1为Spo12相互作用因子。FOB1失活导致中期停滞细胞中Cdc14从核仁过早释放。相反，高水平的FOB1延迟Cdc14从核仁的释放。Fob1与Cfi1/Net1相关联，与此观察结果一致，我们发现大部分Cdc14定位于rDNA重复序列内的Fob1结合区域。最后，我们表明Spo12磷酸化受细胞周期调节并影响其与Fob1的结合。
Fob1作为FEAR网络的负调节因子发挥作用。我们提出Fob1有助于防止后期之前Cdc14与Cfi1/Net1解离，并且后期早期Spo12的激活通过拮抗Fob1功能促进Cdc14从其抑制剂中释放。
