Schmid Maria, Jaedicke Andreas, Du Tung-Gia, Jansen Ralf-Peter
Department of Chemistry and Biochemistry, Gene Center, Ludwig-Maximilians-University Munich, D-81377 Munich, Germany.
Curr Biol. 2006 Aug 8;16(15):1538-43. doi: 10.1016/j.cub.2006.06.025.
Localization of messenger RNAs and local protein synthesis contribute to asymmetric protein distribution not only of cytoplasmic but also of membrane or secreted proteins. Since synthesis of the latter protein classes occurs at the rough endoplasmic reticulum (ER), mRNA localization and distribution of ER should be coordinated. However, this coordination is not yet understood. In yeast, mRNA localization to the growing bud depends on the myosin Myo4p, its adaptor She3p, and the specific RNA binding protein She2p. These proteins mediate the localization of 23 mRNAs including ASH1 mRNA and mRNAs encoding membrane proteins. In addition, Myo4p and She3p are required for segregation of cortical ER to the bud. Here we show, with ASH1 mRNA as a model mRNA, that localizing messenger ribonucleoprotein (mRNP) particles comigrate with tubular ER structures to the bud, which requires the RNA binding protein She2p. Coordinated movement of the ASH1 mRNP with ER tubules but not their association with each other depends on Myo4p and She3p. Subcellular fractionation experiments demonstrate a cosegregation of ER and She2p, which is independent of Myo4p, She3p, or polysomes. Our findings suggest a novel model for mRNA localization that involves association of She2p and mRNPs with ER tubules and myosin-dependent cotransport of tubules and localized mRNPs.
信使核糖核酸（mRNA）的定位和局部蛋白质合成不仅有助于细胞质中蛋白质的不对称分布，也有助于膜蛋白或分泌蛋白的不对称分布。由于后一类蛋白质的合成发生在糙面内质网（ER），因此mRNA的定位与内质网的分布应该相互协调。然而，这种协调机制尚不清楚。在酵母中，mRNA向生长中的芽的定位取决于肌球蛋白Myo4p、其衔接蛋白She3p以及特定的RNA结合蛋白She2p。这些蛋白质介导了包括ASH1 mRNA和编码膜蛋白的mRNA在内的23种mRNA的定位。此外，Myo4p和She3p是皮质内质网向芽分离所必需的。在这里，我们以ASH1 mRNA作为模型mRNA表明，定位的信使核糖核蛋白（mRNP）颗粒与管状内质网结构一起迁移到芽中，这需要RNA结合蛋白She2p。ASH1 mRNP与内质网小管的协同运动而非它们之间的相互结合取决于Myo4p和She3p。亚细胞分级分离实验表明内质网和She2p共分离，这与Myo4p、She3p或多核糖体无关。我们的研究结果提出了一种新的mRNA定位模型，该模型涉及She2p和mRNP与内质网小管的结合以及小管和定位的mRNP的肌球蛋白依赖性共运输。
