Crosstalk between cell-division and cell-growth by the nucleolar proteins with multifunction

核糖体的生物发生是根据细胞增殖机制的变化而严格调控的。然而，人们对核糖体合成和其他细胞系统之间的联系知之甚少。为了阐明这种联系，我们重点研究了两个相互作用的反式作用因子Ebp2和Rrs1，它们是25S rRNA成熟和组装60S核糖体亚基所必需的。(1)Ebp2和Rrs1在核糖体生物发生中的作用：双杂交筛选表明Ebp2与60S和40S核糖体亚基生物发生所必需的反式作用因子相互作用。这些数据表明，Ebp2参与协同调节两个核糖体亚基的合成(JBC，2004)。TAP-纯化和质谱分析表明，Ebp2和Rrs1参与了核糖体前颗粒的不同阶段。我们构建了温度敏感的rrs1突变体，并认为rrs1是60S核糖体亚基核输出所必需的(FEBS Let.，2004)。我们还认为，60S核糖体亚基上L5-5S rRNA的组装与L11通过Rrs1的组装是协调的(NAR 2005)。(2)Ebp2和Rrs1在其他细胞系统中的作用：我们构建了温度敏感的ebp2突变体，表现出对TBZ敏感，细胞形态小，核形状异常，纺锤体短。EGFP-Ebp2p和EGFP-Rrs1p除定位于核仁外，还定位于核周。然而，在ebp2突变细胞中，Ebp2没有定位在核周。我们认为Ebp2p和Rrslp在酵母中具有两种功能：成熟的25S rRNA和在核仁中组装60S核糖体亚基，以及维持核的形状。

Ribosome biogenesis is strictly regulated according to the changes in cell proliferation mechanisms. However, only little is known about the linkage between ribosome synthesis and other cellular systems. To elucidate this linkage, we focused on two trans-acting factors, Ebp2 and Rrsl, which interact with each other and are required for maturation of 25S rRNA and assembly of the 60S ribosomal subunit.(1) Roles of Ebp2 and Rrs1 in ribosome biogenesis: Two-hybrid screening exhibited that Ebp2 interacts with trans-acting factors essential for biogenesis of both 60S and 40S ribosomal subunits. The data suggest that Ebp2 is involved in cooperatively regulating synthesis of both ribosomal subunits (JBC, 2004). TAP-purification and mass spectrometry revealed that Ebp2 and Rrsl are involved in different stage of pre-ribosomal particle. We constructed temperature sensitive rrsl mutants and suggested that Rrs1 is required for nuclear export of the 60S ribosomal subunit (FEBS Lett., 2004). We also suggested that the assembly of L5-5S rRNA on 60S ribosomal subunits coordinates with assembly of L11 via Rrsl (NAR 2005).(2) Roles of Ebp2 and Rrsl in other cellular systems: We constructed temperature sensitive ebp2 mutants exhibiting TBZ-sensitivity, small cell morphology, an aberrant-shaped nucleus and short spindle. EGFP-Ebp2p and EGFP-Rrs1p are localized at the nuclear periphery besides in the nucleolus. However, in the ebp2 mutant cell, Ebp2 was not localized at the nuclear periphery. We suggested that Ebp2p and Rrslp have two functions in yeast; maturation of 25S rRNA and assembly of the 60S ribosomal subunit in the nucleolus and the maintenance of nuclear shape.