Centre for mRNP Biogenesis and Metabolism, Department of Molecular Biology, Aarhus University, CF Møllers Allé 3, Building 1130, DK-8000 Aarhus C, Denmark.
Mol Cell. 2011 Aug 19;43(4):624-37. doi: 10.1016/j.molcel.2011.06.028.
The RNA exosome is a conserved degradation machinery, which obtains full activity only when associated with cofactors. The most prominent activator of the yeast nuclear exosome is the RNA helicase Mtr4p, acting in the context of the Trf4p/Air2p/Mtr4p polyadenylation (TRAMP) complex. The existence of a similar activator(s) in humans remains elusive. By establishing an interaction network of the human nuclear exosome, we identify the trimeric Nuclear Exosome Targeting (NEXT) complex, containing hMTR4, the Zn-knuckle protein ZCCHC8, and the putative RNA binding protein RBM7. ZCCHC8 and RBM7 are excluded from nucleoli, and consistently NEXT is specifically required for the exosomal degradation of promoter upstream transcripts (PROMPTs). We also detect putative homolog TRAMP subunits hTRF4-2 (Trf4p) and ZCCHC7 (Air2p) in hRRP6 and hMTR4 precipitates. However, at least ZCCHC7 function is restricted to nucleoli. Our results suggest that human nuclear exosome degradation pathways comprise modules of spatially organized cofactors that diverge from the yeast model.
RNA 外切体是一种保守的降解机制，只有与辅助因子结合时才能发挥全部活性。酵母核外切体最主要的激活因子是 RNA 解旋酶 Mtr4p，它在 Trf4p/Air2p/Mtr4p 多腺苷酸化（TRAMP）复合物的背景下发挥作用。在人类中是否存在类似的激活因子仍不清楚。通过建立人核外切体的相互作用网络，我们鉴定出三聚体核外切体靶向（NEXT）复合物，包含 hMTR4、Zn 指蛋白 ZCCHC8 和假定的 RNA 结合蛋白 RBM7。ZCCHC8 和 RBM7 被排除在核仁之外，并且 NEXT 复合物特异性地需要用于启动子上游转录物（PROMPTs）的外切体降解。我们还在 hRRP6 和 hMTR4 沉淀中检测到假定的同源 TRAMP 亚基 hTRF4-2（Trf4p）和 ZCCHC7（Air2p）。然而，至少 ZCCHC7 的功能仅限于核仁。我们的结果表明，人类核外切体降解途径包括空间组织辅助因子模块，与酵母模型不同。
