Rosenkrantz M, Alam T, Kim K S, Clark B J, Srere P A, Guarente L P
Mol Cell Biol. 1986 Dec;6(12):4509-15. doi: 10.1128/mcb.6.12.4509-4515.1986.
Saccharomyces cerevisiae contains two genes, CIT1 and CIT2, encoding functional citrate synthase (K.-S. Kim, M. S. Rosenkrantz, and L. Guarente, Mol. Cell. Biol. 6:1936-1942, 1986). We show here that CIT2 encodes a nonmitochondrial form of citrate synthase. The DNA sequence of CIT2 presented provides a possible explanation for why the CIT2 product, unlike the CIT1 product, fails to be imported into mitochondria. While the products of these two genes are highly homologous, they diverge strikingly at their amino termini. The amino terminus of the CIT1 primary translation product extends 39 residues beyond the amino termini of Escherichia coli and porcine citrate synthases. This extension consists of a typical mitochondrial targeting motif. The amino terminus of the CIT2 primary translation product extends 20 residues beyond the amino termini of the E. coli and porcine enzymes. The CIT2-encoded extension is not homologous to that of CIT1, resulting in a nonmitochondrial localization of the product. The CIT2-encoded extension, however, does bear certain similarities to mitochondrial targeting sequences. The possible role of this sequence in targeting this CIT2 product to a nonmitochondrial organelle is discussed.
酿酒酵母含有两个基因，CIT1和CIT2，它们编码功能性柠檬酸合酶（K.-S. Kim、M. S. Rosenkrantz和L. Guarente，《分子细胞生物学》6:1936 - 1942，1986年）。我们在此表明，CIT2编码一种非线粒体形式的柠檬酸合酶。所呈现的CIT2的DNA序列为为何CIT2产物与CIT1产物不同，不能被导入线粒体提供了一种可能的解释。虽然这两个基因的产物高度同源，但它们在氨基末端显著不同。CIT1初级翻译产物的氨基末端比大肠杆菌和猪柠檬酸合酶的氨基末端多延伸39个残基。这个延伸部分包含一个典型的线粒体靶向基序。CIT2初级翻译产物的氨基末端比大肠杆菌和猪酶的氨基末端多延伸20个残基。CIT2编码的延伸部分与CIT1的不同源，导致其产物定位于非线粒体。然而，CIT2编码的延伸部分确实与线粒体靶向序列有某些相似之处。讨论了该序列在将CIT2产物靶向非线粒体细胞器中的可能作用。
