Granneman Sander, Vogelzangs Judith, Lührmann Reinhard, van Venrooij Walther J, Pruijn Ger J M, Watkins Nicholas J
Department of Biochemistry, University of Nijmegen, The Netherlands.
Mol Cell Biol. 2004 Oct;24(19):8600-10. doi: 10.1128/MCB.24.19.8600-8610.2004.
In the nucleolus the U3 snoRNA is recruited to the 80S pre-rRNA processing complex in the dense fibrillar component (DFC). The U3 snoRNA is found throughout the nucleolus and has been proposed to move with the preribosomes to the granular component (GC). In contrast, the localization of other RNAs, such as the U8 snoRNA, is restricted to the DFC. Here we show that the incorporation of the U3 snoRNA into the 80S processing complex is not dependent on pre-rRNA base pairing sequences but requires the B/C motif, a U3-specific protein-binding element. We also show that the binding of Mpp10 to the 80S U3 complex is dependent on sequences within the U3 snoRNA that base pair with the pre-rRNA adjacent to the initial cleavage site. Furthermore, mutations that inhibit 80S complex formation and/or the association of Mpp10 result in retention of the U3 snoRNA in the DFC. From this we propose that the GC localization of the U3 snoRNA is a direct result of its active involvement in the initial steps of ribosome biogenesis.
在核仁中，U3小核仁RNA（snoRNA）被招募到致密纤维组分（DFC）中的80S前体核糖体RNA（pre-rRNA）加工复合体。U3 snoRNA在整个核仁中都有发现，有人提出它会与前核糖体一起移动到颗粒组分（GC）。相比之下，其他RNA，如U8 snoRNA的定位则局限于DFC。在这里我们表明，U3 snoRNA掺入80S加工复合体并不依赖于pre-rRNA碱基配对序列，而是需要B/C基序，这是一个U3特异性的蛋白质结合元件。我们还表明，Mpp10与80S U3复合体的结合依赖于U3 snoRNA中与初始切割位点相邻的pre-rRNA碱基配对的序列。此外，抑制80S复合体形成和/或Mpp10缔合的突变会导致U3 snoRNA保留在DFC中。由此我们提出，U3 snoRNA的GC定位是其积极参与核糖体生物发生初始步骤的直接结果。
