Shou Wenying, Deshaies Raymond J
Division of Biology, 156-29 Howard Hughes Medical Institute, California Institute of Technology, Pasadena, CA 91125, USA.
BMC Genet. 2002 Mar 12;3:4. doi: 10.1186/1471-2156-3-4.
The Mitotic Exit Network (MEN) proteins - including the protein kinase Cdc15 and the protein phosphatase Cdc14 - are essential for exit from mitosis in Saccharomyces cerevisiae. To identify downstream targets of the MEN, we sought telophase arrest bypassed (tab) mutations that bypassed the essential requirement for CDC15. Previous studies identified net1(tab2-1) and CDC14(TAB6-1) as mutations in the RENT complex subunits Net1 and Cdc14, respectively, and revealed that the MEN acts by promoting release of Cdc14 from its nucleolar Net1 anchor during anaphase. However, the remaining tab mutants were not characterized.
Fourteen out of fifteen tab mutants were mapped to three recessive (tab1-tab3) and three dominant (TAB5-TAB7) linkage groups. We show that net1(tab2-1) enables growth of tem1Delta, cdc15Delta, dbf2Delta dbf20Delta, and mob1Delta, but not cdc5Delta or cdc14Delta, arguing that whereas the essential task of the first four genes is to promote exit from mitosis, CDC5 possesses additional essential function(s). net1(tab2-1) but not CDC14(TAB6-1) resulted in a high rate of chromosome loss, indicating that Net1 promotes accurate chromosome segregation in addition to its multiple known roles. Finally, TAB1 was shown to be MTR10, a gene encoding nuclear transport receptor/adaptor. In some of the tab mutants including mtr10(tab1-1), defective nuclear export of the ribosomal protein Rpl11b was observed. Furthermore, the transport-defective -31 allele of the karyopherin SRP1, but not the transport competent -49 allele, exhibited a tab phenotype.
Transport-defective mutations in two karyopherins can bypass cdc15Delta, suggesting that the function of the MEN is to promote mitotic exit by regulating nuclear transport.
有丝分裂退出网络（MEN）蛋白——包括蛋白激酶Cdc15和蛋白磷酸酶Cdc14——对于酿酒酵母从有丝分裂中退出至关重要。为了鉴定MEN的下游靶点，我们寻找了能绕过对CDC15的必需需求的末期阻滞绕过（tab）突变。先前的研究分别鉴定出net1（tab2 - 1）和CDC14（TAB6 - 1）是RENT复合物亚基Net1和Cdc14中的突变，并揭示MEN在后期通过促进Cdc14从其核仁Net1锚定物中释放而起作用。然而，其余的tab突变体尚未得到表征。
十五个tab突变体中的十四个被定位到三个隐性（tab1 - tab3）和三个显性（TAB5 - TAB7）连锁群。我们表明net1（tab2 - 1）能使tem1Δ、cdc15Δ、dbf2Δ dbf20Δ和mob1Δ生长，但不能使cdc5Δ或cdc14Δ生长，这表明前四个基因的基本任务是促进有丝分裂退出，而CDC5具有额外的基本功能。net1（tab2 - 1）而非CDC14（TAB6 - 1）导致染色体丢失率很高，表明Net1除了其多个已知作用外，还促进准确的染色体分离。最后，TAB1被证明是MTR10，一个编码核转运受体/衔接蛋白的基因。在包括mtr10（tab1 - 1）在内的一些tab突变体中，观察到核糖体蛋白Rpl11b的核输出存在缺陷。此外，核转运蛋白SRP1的运输缺陷型 - 31等位基因而非运输功能正常的 - 49等位基因表现出tab表型。
两种核转运蛋白中的运输缺陷型突变可以绕过cdc15Δ，这表明MEN的功能是通过调节核转运来促进有丝分裂退出。
