McBratney Susan, Winey Mark
Department of Molecular, Cellular and Developmental Biology, University of Colorado, Boulder 80309-0347, USA.
Genetics. 2002 Oct;162(2):567-78. doi: 10.1093/genetics/162.2.567.
Mutation of either the yeast MPS2 or the NDC1 gene leads to identical spindle pole body (SPB) duplication defects: The newly formed SPB is improperly inserted into the nuclear envelope (NE), preventing the cell from forming a bipolar mitotic spindle. We have previously shown that both MPS2 and NDC1 encode integral membrane proteins localized at the SPB. Here we show that CUE1, previously known to have a role in coupling ubiquitin conjugation to ER degradation, is an unusual dosage suppressor of mutations in MPS2 and NDC1. Cue1p has been shown to recruit the soluble ubiquitin-conjugating enzyme, Ubc7p, to the cytoplasmic face of the ER membrane where it can ubiquitinate its substrates and target them for degradation by the proteasome. Both mps2-1 and ndc1-1 are also suppressed by disruption of UBC7 or its partner, UBC6. The Mps2-1p mutant protein level is markedly reduced compared to wild-type Mps2p, and deletion of CUE1 restores the level of Mps2-1p to nearly wild-type levels. Our data indicate that Mps2p may be targeted for degradation by the ER quality control pathway.
酵母MPS2基因或NDC1基因的突变会导致相同的纺锤体极体（SPB）复制缺陷：新形成的SPB无法正确插入核膜（NE），从而阻止细胞形成双极有丝分裂纺锤体。我们之前已经表明，MPS2和NDC1都编码定位于SPB的整合膜蛋白。在此我们表明，之前已知在将泛素缀合与内质网降解偶联过程中起作用的CUE1，是MPS2和NDC1突变的一种不同寻常的剂量抑制因子。已证明Cue1p可将可溶性泛素缀合酶Ubc7p募集到内质网膜的胞质面，在那里它可以将其底物泛素化并将它们靶向蛋白酶体进行降解。UBC7或其伙伴UBC6的破坏也能抑制mps2-1和ndc1-1。与野生型Mps2p相比，Mps2-1p突变蛋白水平显著降低，而缺失CUE1可将Mps2-1p水平恢复到几乎野生型水平。我们的数据表明，Mps2p可能被内质网质量控制途径靶向降解。
