Figueroa P, Holuigue L, Araya A, Jordana X
Departamento de Genética Molecular y Microbiología, Facultad de Ciencias Biológicas, P. Universidad Católica de Chile, Casilla 114-D, Santiago, Chile.
Biochem Biophys Res Commun. 2000 May 10;271(2):380-5. doi: 10.1006/bbrc.2000.2644.
In maize, the functional gene encoding mitochondrial ribosomal protein S14 (rps14) has been translocated to the nucleus where it became integrated between both exons of a gene encoding the iron-sulfur subunit of succinate dehydrogenase (sdh2). Two transcripts are generated from this locus by alternative splicing. One transcript encodes a precursor for a functional SDH2 protein, while the second transcript encodes a chimeric SDH2(t)-RPS14 precursor protein. In this paper we show that the same mitochondrial targeting presequence is able to direct the import of both precursors into isolated mitochondria and is removed during import. This processing event generates a 28 kDa protein from the SDH2 precursor, which corresponds to the iron-sulfur subunit of respiratory complex II present in maize mitochondria. In addition to cleavage of the presequence, the chimeric precursor undergoes proteolytical processing between SDH2 and RPS14. This processing generates RPS14, which is found assembled into mitochondrial ribosomes, and a truncated SDH2 protein which is degraded. Therefore, our results support a role of the SDH2 domain in the chimeric precursor only in providing a mitochondrial targeting function for RPS14.
在玉米中，编码线粒体核糖体蛋白S14（rps14）的功能基因已转移至细胞核，整合到琥珀酸脱氢酶（sdh2）铁硫亚基编码基因的两个外显子之间。通过可变剪接从该位点产生两种转录本。一种转录本编码功能性SDH2蛋白的前体，而第二种转录本编码嵌合SDH2(t)-RPS14前体蛋白。在本文中，我们表明相同的线粒体靶向前序列能够将两种前体导入分离的线粒体，并在导入过程中被去除。这一加工事件从SDH2前体产生一个28 kDa的蛋白，它对应于玉米线粒体中呼吸复合物II的铁硫亚基。除了前序列的切割外，嵌合前体在SDH2和RPS14之间还会进行蛋白水解加工。这一加工产生了组装在线粒体核糖体中的RPS14，以及一个被降解的截短SDH2蛋白。因此，我们的结果支持嵌合前体中SDH2结构域仅在为RPS14提供线粒体靶向功能方面发挥作用。
