Centre de Génétique Moléculaire du CNRS, FRE3144, FRC3115, Ave de la Terrasse, 91198, Gif-sur-Yvette, France.
Mol Genet Genomics. 2010 Feb;283(2):111-22. doi: 10.1007/s00438-009-0501-3. Epub 2009 Dec 5.
In Saccharomyces cerevisiae, the RAM network is involved in cell separation after cytokinesis, cell integrity and cell polarity. The key function of this network is the regulation of the activity of the protein kinase Cbk1p, which is a member of the conserved NDR kinase family. Cbk1p function is controlled by its sub-cellular localization and at least two phosphorylation events: an auto phosphorylation in the kinase domain (S570) and the phosphorylation of a C-terminal hydrophobic motif by an upstream kinase (T743). After a UV mutagenesis, we have isolated 115 independent extragenic suppressors of four ram mutations: tao3, hym1, kic1 and sog2. Over 50% of the suppressors affect a single residue in Cbk1p (S745F), which is close to the phosphorylation site in the hydrophobic motif. Our results show that the CBK1-S745F allele leads to a constitutively active form of Cbk1p that is independent of the upstream RAM network. We hypothesize that the mutant Cbk1-S745Fp mimics the effect of the phosphorylation of T743.
在酿酒酵母中，RAM 网络参与胞质分裂后细胞分离、细胞完整性和细胞极性。该网络的关键功能是调节蛋白激酶 Cbk1p 的活性，Cbk1p 是保守的 NDR 激酶家族的成员。Cbk1p 的功能受其亚细胞定位和至少两个磷酸化事件控制：激酶结构域中的自身磷酸化（S570）和上游激酶对 C 端疏水基序的磷酸化（T743）。通过 UV 诱变，我们分离了四个 ram 突变（tao3、hym1、kic1 和 sog2）的 115 个独立的外显子抑制子。超过 50%的抑制子影响 Cbk1p 中的单个残基（S745F），该残基靠近疏水基序中的磷酸化位点。我们的结果表明，CBK1-S745F 等位基因导致 Cbk1p 的组成型激活形式，不依赖于上游 RAM 网络。我们假设突变的 Cbk1-S745Fp 模拟了 T743 磷酸化的效果。
