Wang Chien-Chia, Chang Kuang-Jung, Tang Huei-Lin, Hsieh Chia-Jung, Schimmel Paul
Department of Life Science, National Central University, Chung-Li, Taiwan 32054.
Biochemistry. 2003 Feb 18;42(6):1646-51. doi: 10.1021/bi025964c.
Previous studies showed that yeast VAS1 encodes both the cytoplasmic and mitochondrial forms of valyl-tRNA synthetase (ValRS), using alternative transcription and translation. The ValRS isoforms have identical polypeptide sequences, except for a 46-amino acid leader peptide that functions as a mitochondrial targeting signal. Although the two forms of the enzyme exhibit indistinguishable tRNA specificities in vitro, they cannot substitute for each other in vivo because of their different localizations. Here we show that the 46-residue leader sequence can be divided into two nonoverlapping peptides, each of which retains the ability to target the enzyme into mitochondria. The engineered proteins (with truncated leader sequences) are dual-targeted, rescuing both the cytoplasmic and mitochondrial defects of a vas1 knockout strain. Thus, in addition to alternative splicing and alternative translation initiation as mechanisms by which a single gene can encode cytoplasmic and mitochondrial activities, the inherent characteristics of a single polypeptide may enable it to be distributed simultaneously between two cellular compartments. This mechanism may explain how certain other single genes in Saccharomyces cerevisiae provide dual functions.
先前的研究表明，酵母VAS1通过选择性转录和翻译编码缬氨酰 - tRNA合成酶（ValRS）的细胞质和线粒体形式。ValRS同工型具有相同的多肽序列，除了一个作为线粒体靶向信号的46个氨基酸的前导肽。尽管这两种形式的酶在体外表现出难以区分的tRNA特异性，但由于它们的定位不同，它们在体内不能相互替代。在这里，我们表明46个残基的前导序列可以分为两个不重叠的肽段，每个肽段都保留了将酶靶向线粒体的能力。工程化蛋白（具有截短的前导序列）是双靶向的，挽救了vas1敲除菌株的细胞质和线粒体缺陷。因此，除了选择性剪接和选择性翻译起始作为单个基因可编码细胞质和线粒体活性的机制外，单个多肽的固有特性可能使其能够同时分布在两个细胞区室之间。这种机制可能解释了酿酒酵母中的某些其他单个基因如何提供双重功能。
