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首页> 外文期刊>Journal of Molecular Biology >Trypanosoma brucei 5 ' ETS A '-cleavage is directed by 3 '-adjacent sequences, but not two U3 snoRNA-binding elements, which are all required for subsequent pre-small subunit rRNA processing events
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Trypanosoma brucei 5 ' ETS A '-cleavage is directed by 3 '-adjacent sequences, but not two U3 snoRNA-binding elements, which are all required for subsequent pre-small subunit rRNA processing events

机译：布氏锥虫5'ETS A'切割是由3'相邻序列指导的，但不是两个U3 snoRNA结合元件，所有这些都是随后的小亚基rRNA加工事件所必需的

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Trypanosoma brucei pre-rRNA processing commences by cleavage near the 5' end of 5.8 S sequences. The 5' external transcribed spacer (FETS) is removed from pre-small subunit (SSU) rRNAs by sequential cleavages at internal A' and AO sites, and Al at the 5' end of SSU rRNA. The A' and AO sites positionally resemble the U3 small nucleolar RNA-dependent, primary pre-rRNA cleavages of vertebrates and yeast, respectively. Uniquely in T. brucei, two U3-crosslinkable FETS sites are essential for SSU rRNA production: site1b is novel in its 3' location to the A' site, and site3 lies upstream of AO in a position analogous to the yeast U3-binding site. Here, in vivo analysis of mutated 5'ETS sequences shows that sequences 5' to the A' site are not needed for A' cleavage or SSU rRNA production. A' cleavage is linked to, but is not sufficient to trigger, downstream pre-SSU rRNA processing events. These events require an intact 11 nt sequence, 3'-adjacent to A', which directs efficient and accurate A' cleavage. Neither the A' nearby site1b nor the site3 U3-binding elements affect A processing, yet each is required for AO and A' cleavage, and SSU rRNA production. The same U3 3' hinge bases evidently bind a core element, UGUu/gGGU, within site1a and site3; the U3-site1b interaction is less reliant on base-pairing than the U3-site3 interaction. As yeast U3 5' hinge bases pair to FETS sequences, it is clear that distinct U3 hinge regions can interact at both novel and related FETS sites to promote 3'-proximal FETS processing events in diverse organisms. The T. brucei data fit a model wherein processing factors assemble at the 5'ETS site1a to affect A' cleavage and stabilize a U3-site1b complex, which may work in concert with the downstream U3-site3 complex to assist processing events leading to ribosomal SSU production.
机译：布氏锥虫前rRNA的加工开始于5.8 S序列5'末端附近的切割。通过在内部A'和AO位点进行顺序切割，以及在SSU rRNA的5'端进行Al切割，从小前亚基（SSU）rRNA中去除5'外部转录间隔区（FETS）。 A'和AO位点的位置分别类似于脊椎动物和酵母的U3小核仁RNA依赖性初级rRNA裂解。在T. brucei中，两个U3可交联的FETS位点对于SSU rRNA的生产是必不可少的：site1b在其3'位置相对于A'位是新颖的，而site3位于AO上游，其位置类似于酵母U3结合位点。在这里，对突变的5'ETS序列的体内分析表明，A'切割或SSU rRNA产生不需要A'位点的5'序列。 A'切割与下游SSU前rRNA加工事件相关，但不足以触发下游。这些事件需要一个完整的11 nt序列，与A'相邻3'，可指导有效和准确的A'切割。 A'附近的site1b或site3的U3结合元件都不会影响A的加工，但每个都需要AO和A'裂解以及SSU rRNA的产生。相同的U3 3'铰链碱基显然在site1a和site3中绑定了核心元素UGUu / gGGU;与U3-site3相互作用相比，U3-site1b相互作用对碱基配对的依赖性较小。当酵母U3 5'铰链碱基与FETS序列配对时，很明显，不同的U3铰链区域可以在新的和相关的FETS位点相互作用，从而促进多种生物中3'-近端FETS加工事件。 T. brucei数据拟合模型，其中加工因子在5'ETS site1a聚集以影响A'裂解并稳定U3-site1b复合物，该复合物可与下游U3-site3复合物协同工作，以协助导致核糖体的加工事件SSU生产。

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