Brengues Muriel, Parker Roy
Department of Molecular and Cellular Biology, Howard Hughes Medical Institute, University of Arizona, Tucson, AZ 85721-0106, USA.
Mol Biol Cell. 2007 Jul;18(7):2592-602. doi: 10.1091/mbc.e06-12-1149. Epub 2007 May 2.
Recent experiments have shown that mRNAs can move between polysomes and P-bodies, which are aggregates of nontranslating mRNAs associated with translational repressors and the mRNA decapping machinery. The transitions between polysomes and P-bodies and how the poly(A) tail and the associated poly(A) binding protein 1 (Pab1p) may affect this process are unknown. Herein, we provide evidence that poly(A)(+) mRNAs can enter P-bodies in yeast. First, we show that both poly(A)(-) and poly(A)(+) mRNA become translationally repressed during glucose deprivation, where mRNAs accumulate in P-bodies. In addition, both poly(A)(+) transcripts and/or Pab1p can be detected in P-bodies during glucose deprivation and in stationary phase. Cells lacking Pab1p have enlarged P-bodies, suggesting that Pab1p plays a direct or indirect role in shifting the equilibrium of mRNAs away from P-bodies and into translation, perhaps by aiding in the assembly of a type of mRNP within P-bodies that is poised to reenter translation. Consistent with this latter possibility, we observed the translation initiation factors (eIF)4E and eIF4G in P-bodies at a low level during glucose deprivation and at high levels in stationary phase. Moreover, Pab1p exited P-bodies much faster than Dcp2p when stationary phase cells were given fresh nutrients. Together, these results suggest that polyadenylated mRNAs can enter P-bodies, and an mRNP complex including poly(A)(+) mRNA, Pab1p, eIF4E, and eIF4G2 may represent a transition state during the process of mRNAs exchanging between P-bodies and translation.
最近的实验表明，信使核糖核酸（mRNA）可以在多核糖体和P小体之间移动，P小体是与翻译抑制因子和mRNA脱帽机制相关的非翻译mRNA聚集体。多核糖体和P小体之间的转变以及聚腺苷酸（poly(A)）尾巴和相关的聚腺苷酸结合蛋白1（Pab1p）如何影响这一过程尚不清楚。在此，我们提供证据表明，聚腺苷酸（poly(A)）阳性mRNA可以进入酵母中的P小体。首先，我们表明，在葡萄糖剥夺期间，聚腺苷酸（poly(A)）阴性和聚腺苷酸（poly(A)）阳性mRNA都会受到翻译抑制，此时mRNA会在P小体中积累。此外，在葡萄糖剥夺期间和稳定期，P小体中都可以检测到聚腺苷酸（poly(A)）阳性转录本和/或Pab1p。缺乏Pab1p的细胞具有更大的P小体，这表明Pab1p在将mRNA的平衡从P小体转移到翻译过程中发挥直接或间接作用，可能是通过帮助在P小体中组装一种准备重新进入翻译的mRNA核糖核蛋白（mRNP）。与后一种可能性一致，我们观察到在葡萄糖剥夺期间，翻译起始因子（eIF）4E和eIF4G在P小体中的水平较低，而在稳定期则较高。此外，当给稳定期细胞提供新鲜营养时，Pab1p离开P小体的速度比Dcp2p快得多。总之，这些结果表明，多聚腺苷酸化的mRNA可以进入P小体，并且包括聚腺苷酸（poly(A)）阳性mRNA、Pab1p、eIF4E和eIF4G2的mRNP复合物可能代表mRNA在P小体和翻译之间交换过程中的一种过渡状态。
