Metal ion catalysis during group II intron self-splicing: parallels with the spliceosome
Metal ion catalysis during group II intron self-splicing: parallels with the spliceosome
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DOI：
10.1101/gad.13.13.1729
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发表时间：
1999-07-01
影响因子：
10.5
通讯作者：
Piccirilli, JA
中科院分区：
文献类型：
--
作者：
Sontheimer, EJ;Gordon, PM;Piccirilli, JA
剪接体和自剪接II组内含子核酶执行的相同反应途径促使人们认为两者可能来自一个共同的分子祖先。然而，II组内含子和剪接体小核rna之间的最小序列和结构相似性使这一提议受到质疑。因此，比较II类自剪接内含子和剪接体之间的机制对于确定这两种剪接机制是否相关具有重要意义。在这里，我们发现在II族内含子的5‘剪接位点上的3’-硫取代在剪接的第一步引起金属特异性开关。相反，3'-硫取代对顺式拼接第二步的金属特异性没有显著影响。第二步的隔离揭示了在顺式剪接反应期间被掩盖的金属特异性开关。这些结果表明，II族内含子核酶是一种金属酶，在自剪接的两个步骤中使用催化金属离子来离开基团稳定。此外，由于剪接体内含子的3'-硫取代与II族内含子的顺式剪接具有完全相同的效果，因此这些结果提供了这两种系统所采用的催化机制之间惊人的相似之处。
The identical reaction pathway executed by the spliceosome and self-splicing group II intron ribozymes has prompted the idea that both may be derived from a common molecular ancestor. The minimal sequence and structural similarities between group II introns and the spliceosomal small nuclear RNAs, however, have left this proposal in question. Mechanistic comparisons between group II self-splicing introns and the spliceosome are therefore important in determining whether these two splicing machineries may be related. Here we show that 3'-sulfur substitution at the 5' splice site of a group II intron causes a metal specificity switch during the first step of splicing. In contrast, 3'-sulfur substitution has no significant effect on the metal specificity of the second step of cis-splicing. Isolation of the second step uncovers a metal specificity switch that is masked during the cis-splicing reaction. These results demonstrate that group II intron ribozymes are metalloenzymes that use a catalytic metal ion for leaving group stabilization during both steps of self-splicing. Furthermore, because 3'-sulfur substitution of a spliceosomal intron has precisely the same effects as were observed during cis-splicing of the group II intron, these results provide striking parallels between the catalytic mechanisms employed by these two systems.