Gelperin D, Horton L, Beckman J, Hensold J, Lemmon S K
Department of Molecular Biology and Microbiology, Case Western Reserve University School of Medicine, Cleveland, Ohio 44106, USA.
RNA. 2001 Sep;7(9):1268-83. doi: 10.1017/s1355838201013073.
Bms1p and Tsr1p define a novel family of proteins required for synthesis of 40S ribosomal subunits in Saccharomyces cerevisiae. Both are essential and localize to the nucleolus. Tsr1p shares two extended regions of similarity with Bms1p, but the two proteins function at different steps in 40S ribosome maturation. Inactivation of Bms1p blocks at an early step, leading to disappearance of 20S and 18S rRNA precursors. Also, slight accumulation of an aberrant 23S product and significant 35S accumulation are observed, indicating that pre-rRNA processing at sites A0, A1, and A2 is inhibited. In contrast, depletion of Tsr1p results in accumulation of 20S rRNA. Because processing of 20S to 18S rRNA occurs in the cytoplasm, this suggests that Tsr1p is required for assembly of a transport- or maturation-competent particle or is specifically required for transport of 43S pre-ribosomal particles, but not 60S ribosome precursors, from the nucleus to the cytosol. Finally, Bms1p is a GTP-binding protein, the first found to function in ribosome assembly or rRNA processing.
Bms1p和Tsr1p定义了酿酒酵母中40S核糖体亚基合成所需的一个新的蛋白质家族。两者都是必需的，且定位于核仁。Tsr1p与Bms1p有两个相似的延伸区域，但这两种蛋白质在40S核糖体成熟的不同步骤发挥作用。Bms1p失活在早期步骤受阻，导致20S和18S rRNA前体消失。此外，观察到异常23S产物有轻微积累以及35S显著积累，表明A0、A1和A2位点的前体rRNA加工受到抑制。相比之下，Tsr1p缺失导致20S rRNA积累。由于20S到18S rRNA的加工发生在细胞质中，这表明Tsr1p是组装具有运输或成熟能力的颗粒所必需的，或者是43S核糖体前体颗粒从细胞核运输到细胞质所特别需要的，但不是60S核糖体前体所必需的。最后，Bms1p是一种GTP结合蛋白，是第一个被发现参与核糖体组装或rRNA加工的此类蛋白。
