Ho Y, Kim S J, Waring R B
Department of Biology, Temple University, Philadelphia, PA 19122, USA.
Proc Natl Acad Sci U S A. 1997 Aug 19;94(17):8994-9. doi: 10.1073/pnas.94.17.8994.
Some group I introns self-splice in vitro, but almost all are thought to be assisted by proteins in vivo. Mutational analysis has shown that the splicing of certain group I introns depends upon a maturase protein encoded by the intron itself. However the effect of a protein on splicing can be indirect. We now provide evidence that a mitochondrial intron-encoded protein from Aspergillus nidulans directly facilitates splicing in vitro. This demonstrates that a maturase is an RNA splicing protein. The protein-assisted reaction is as fast as that of any other known group I intron. Interestingly the protein is also a DNA endonuclease, an activity required for intron mobilization. Mobile elements frequently encode proteins that promote their propagation. Intron-encoded proteins that also assist RNA splicing would facilitate both the transposition and horizontal transmission of introns.
一些I类内含子在体外可自我剪接，但几乎所有I类内含子在体内都被认为需要蛋白质的协助。突变分析表明，某些I类内含子的剪接依赖于内含子自身编码的成熟酶蛋白。然而，蛋白质对剪接的作用可能是间接的。我们现在提供证据表明，来自构巢曲霉的一种线粒体内含子编码蛋白在体外可直接促进剪接。这证明成熟酶是一种RNA剪接蛋白。该蛋白质辅助的反应与任何其他已知I类内含子的反应一样快。有趣的是，该蛋白质也是一种DNA内切酶，这是内含子移动所需的一种活性。移动元件经常编码促进其传播的蛋白质。同时协助RNA剪接的内含子编码蛋白将有利于内含子的转座和水平转移。
