The final step in the formation of 25S rRNA in Saccharomyces cerevisiae is performed by 5′→3′ exonucleases
The final step in the formation of 25S rRNA in Saccharomyces cerevisiae is performed by 5′→3′ exonucleases
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DOI：
10.1017/s1355838200001540
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发表时间：
2000-12-01
期刊：
影响因子：
4.5
通讯作者：
Raué, HA
中科院分区：
文献类型：
--
作者：
Geerlings, TH;Vos, JC;Raué, HA
酿酒酵母中两个大亚基 rRNA 物种形成的最后阶段是从 27SB 前体中去除内部转录间隔区 2 (ITS2)。这种去除是由 ITS2 大约中间的核酸内切裂解启动的。由此产生的 7S pre-rRNA 易于检测，然后通过许多 3'->5' 核酸外切酶的协同作用转化为 5.8S rRNA，其中许多核酸外切酶是外泌体的一部分。迄今为止，尚未检测到由 ITS2 中初始切割产生的 25S rRNA 的互补前体，并且其转化为成熟物种的方式也是未知的。使用携带主要 5'→3' 外切核酸酶 Rat1p 和 Xrn1p 的野生型和突变型等位基因的不同组合的各种酵母菌株，我们现在证明了短命的 25.5S pre-rRNA 的存在，其 5' 末端位于先前映射的 7S pre-rRNA 3' 末端的下游。 25.5S pre-rRNA 通过快速核酸外切修剪（主要由 Rat1p 进行）转化为成熟的 25S rRNA。然而，在 Rat1p 不存在的情况下，Xrn1p 也可以从 25.5S pre-rRNA 中去除 ITS2 序列，尽管效率稍低。
The final stage in the formation of the two large subunit rRNA species in Saccharomyces cerevisiae is the removal of internal transcribed spacer 2 (ITS2) from the 27SB precursors. This removal is initiated by endonucleolytic cleavage approximately midway in ITS2. The resulting 7S pre-rRNA, which is easily detectable, is then converted into 5.8S rRNA by the concerted action of a number of 3' --> 5' exonucleases, many of which are part of the exosome. So far the complementary precursor to 25S rRNA resulting from the initial cleavage in ITS2 has not been detected and the manner of its conversion into the mature species is unknown. Using various yeast strains that carry different combinations of wild-type and mutant alleles of the major 5' --> 3' exonucleases Rat1p and Xrn1p, we now demonstrate the existence of a short-lived 25.5S pre-rRNA whose 5' end is located closely downstream of the previously mapped 3' end of 7S pre-rRNA. The 25.5S pre-rRNA is converted into mature 25S rRNA by rapid exonucleolytic trimming, predominantly carried out by Rat1p. In the absence of Rat1p, however, the removal of the ITS2 sequences from 25.5S pre-rRNA can also be performed by Xrn1p, albeit somewhat less efficiently.