Centro de Biología Molecular Severo Ochoa, Consejo Superior de Investigaciones Científicas and Universidad Autónoma de Madrid, Cantoblanco E-28049 Madrid, Spain.
Nucleic Acids Res. 2009 Dec;37(22):7519-32. doi: 10.1093/nar/gkp806.
Mrt4 is a nucleolar component of the ribosome assembly machinery that shares notable similarity and competes for binding to the 25S rRNA GAR domain with the ribosomal protein P0. Here, we show that loss of function of either P0 or Mrt4 results in a deficit in 60S subunits, which is apparently due to impaired rRNA processing of 27S precursors. Mrt4, which shuttles between the nucleus and the cytoplasm, defines medium pre-60S particles. In contrast, P0 is absent from medium but present in late/cytoplasmic pre-60S complexes. The absence of Mrt4 notably increased the amount of P0 in nuclear Nop7-TAP complexes and causes P0 assembly to medium pre-60S particles. Upon P0 depletion, Mrt4 is relocated to the cytoplasm within aberrant 60S subunits. We conclude that Mrt4 controls the position and timing of P0 assembly. In turn, P0 is required for the release of Mrt4 and exchanges with this factor at the cytoplasm. Our results also suggest other P0 assembly alternatives.
Mrt4 是核糖体组装机器的核仁成分，与核糖体蛋白 P0 具有显著的相似性，并竞争结合到 25S rRNA GAR 结构域。在这里，我们表明 P0 或 Mrt4 的功能丧失都会导致 60S 亚基的减少，这显然是由于 27S 前体 rRNA 加工受损所致。Mrt4 在核和细胞质之间穿梭，定义了中等前 60S 颗粒。相比之下，P0 不存在于中等前体中，但存在于晚期/细胞质前 60S 复合物中。Mrt4 的缺失显著增加了核 Nop7-TAP 复合物中 P0 的含量，并导致 P0 组装到中等前 60S 颗粒中。在 P0 耗尽后，Mrt4 重新定位到细胞质中的异常 60S 亚基中。我们得出结论，Mrt4 控制 P0 组装的位置和时间。反过来，P0 对于 Mrt4 的释放以及与细胞质中该因子的交换是必需的。我们的结果还表明存在其他 P0 组装的替代途径。
