van Loon A P, Young E T
EMBO J. 1986 Jan;5(1):161-5. doi: 10.1002/j.1460-2075.1986.tb04191.x.
The yeast Saccharomyces cerevisiae contains three alcohol dehydrogenase isoenzymes (ADHI-ADHIII), two in the cytoplasm (ADHI and ADHII) and one in the mitochondrion (ADHIII). Sequence comparison of the corresponding nuclear genes showed that these three proteins are 80-90% identical except for a 27-amino acid extension at the amino terminus of ADHIII. Here we demonstrate that ADHIII is located inside the mitochondrial inner membrane. We also show, using gene fusions, that the amino terminus of ADHIII contains the information for targeting the protein to and transporting it into the mitochondrion. The mitochondrial isoenzyme ADHIII can be converted into a cytosolic protein by deleting its first 28 amino acids. Conversely, the cytoplasmic isoenzyme ADHII can be converted into a mitochondrial isoenzyme by replacing its first 21 amino acids with the first 48 amino acids of ADHIII. We conclude that ADHII is a cytosolic protein because it lacks an amino-terminal targeting sequence for the mitochondrion and that ADHIII is a mitochondrial protein because it contains a mitochondrial targeting sequence.
酿酒酵母含有三种乙醇脱氢酶同工酶（ADH I - ADH III），两种存在于细胞质中（ADH I和ADH II），一种存在于线粒体中（ADH III）。对相应核基因的序列比较表明，这三种蛋白质除了ADH III氨基末端有一个27个氨基酸的延伸外，80 - 90%是相同的。在这里，我们证明ADH III位于线粒体内膜内部。我们还利用基因融合表明，ADH III的氨基末端包含将该蛋白质靶向并转运到线粒体中的信息。通过删除其前28个氨基酸，线粒体同工酶ADH III可以转化为胞质蛋白。相反，通过将细胞质同工酶ADH II的前21个氨基酸替换为ADH III的前48个氨基酸，ADH II可以转化为线粒体同工酶。我们得出结论，ADH II是一种胞质蛋白，因为它缺乏线粒体的氨基末端靶向序列，而ADH III是一种线粒体蛋白，因为它含有线粒体靶向序列。
