snoRNA nuclear import and potential for cotranscriptional function in pre-rRNA processing
snoRNA nuclear import and potential for cotranscriptional function in pre-rRNA processing
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DOI：
10.1017/s1355838201001625
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发表时间：
2001-02-01
期刊：
影响因子：
4.5
通讯作者：
Peculis, BA
中科院分区：
文献类型：
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作者：
Peculis, BA
几种snoRNA对于从大前体分子产生成熟形式的18 S、5.8S和28 S rRNA所需的切割事件序列是必需的。在缺席！在U22中，成熟的18 S rRNA不能积累; US snoRNA对于5.8S和28 S rRNA的积累都是必需的。snoRNA促进这些切割事件的机制尚不清楚，可能包括直接切割或辅助核糖体组装的速率或效率。为了更多地了解snoRNA介导的前体rRNA加工的机制，对爪蟾卵母细胞中前体rRNA加工的动力学进行了检查。在细胞质注射相应的体外合成的snoRNA后，可以在snoRNA耗尽的卵母细胞中恢复正确的前rRNA加工。在这些snoRNA拯救实验中前rRNA加工的动力学分析表明，成熟rRNA的积累速率比未处理的卵母细胞中所见的慢。snoRNA以低于用作输入对照的U1 snRNA的速率和总体效率输入到细胞核中。然而，在通过放射自显影术在细胞核中直接检测到snoRNA之前几小时，细胞核中存在足够水平的snoRNA以产生功能表型（拯救rRNA加工）。这表明细胞核中非常少量的snoRNA足以进行拯救。最后，使用转录抑制剂来分离转录和加工。未能拯救snoRNA介导的预积累前体的加工与其中US和U22必须在pre-rRNA的转录期间存在的情况一致。
Several snoRNAs are essential for the sequence of cleavage events required to produce the mature forms of 18S, 5.8S, and 28S rRNA from the large precursor molecule. In the absence! of U22, mature 18S rRNA fails to accumulate; US snoRNA is essential for accumulation of both 5.8S and 28S rRNA, The mechanisms by which snoRNAs facilitate these cleavage events is not known and might include direct cleavage or assisting the rate or efficiency of ribosome assembly. To learn more about the mechanisms of snoRNA-mediated pre-rRNA processing, an examination of the kinetics of pre-rRNA processing in Xenopus oocytes was undertaken. Correct pre-rRNA processing can be restored in snoRNA-depleted oocytes following cytoplasmic injection of the corresponding in vitro-synthesized snoRNA, Analysis of the kinetics of pre-rRNA processing in these snoRNA-rescue experiments demonstrated that the rate of accumulation of mature rRNAs was slower than that seen in untreated oocytes. The snoRNAs were imported into the nucleus at a rate and overall efficiency less than that of U1 snRNA, used as a control for import. However, sufficient levels of snoRNA were present in the nucleus to yield a functional phenotype (rescue of rRNA processing) several hours before the snoRNAs were directly detectable in the nucleus via autoradiography, This indicated that very low amounts of the snoRNA in the nucleus were sufficient for rescue. Finally, transcriptional inhibitors were used to separate transcription and processing, Failure to rescue snoRNA-mediated processing of pre-accumulated precursors is consistent with a scenario in which US and U22 must be present during transcription of pre-rRNA.