Singh K K, Small G M, Lewin A S
Department of Immunology and Medical Microbiology, College of Medicine, University of Florida, Gainesville 32601.
Mol Cell Biol. 1992 Dec;12(12):5593-9. doi: 10.1128/mcb.12.12.5593-5599.1992.
The tripeptide serine-lysine-leucine (SKL) occurs at the carboxyl terminus of many peroxisomal proteins and serves as a peroxisomal targeting signal. Saccharomyces cerevisiae has two isozymes of citrate synthase. The peroxisomal form, encoded by CIT2, terminates in SKL, while the mitochondrial form, encoded by CIT1, begins with an amino-terminal mitochondrial signal sequence and ends in SKN. We analyzed the importance of SKL as a topogenic signal for citrate synthase, using oleate to induce peroxisomes and density gradients to fractionate organelles. Our experiments revealed that SKL was necessary for directing citrate synthase to peroxisomes. C-terminal SKL was also sufficient to target a leaderless version of mitochondrial citrate synthase to peroxisomes. Deleting this tripeptide from the CIT2 protein caused peroxisomal citrate synthase to be missorted to mitochondria. These experiments suggest that the CIT2 protein contains a cryptic mitochondrial targeting signal.
三肽丝氨酸 - 赖氨酸 - 亮氨酸（SKL）存在于许多过氧化物酶体蛋白的羧基末端，作为过氧化物酶体靶向信号。酿酒酵母有两种柠檬酸合酶同工酶。由CIT2编码的过氧化物酶体形式以SKL结尾，而由CIT1编码的线粒体形式以氨基末端线粒体信号序列开始并以SKN结尾。我们使用油酸诱导过氧化物酶体并通过密度梯度分离细胞器，分析了SKL作为柠檬酸合酶拓扑信号的重要性。我们的实验表明，SKL是将柠檬酸合酶导向过氧化物酶体所必需的。C末端的SKL也足以将无引导序列的线粒体柠檬酸合酶靶向到过氧化物酶体。从CIT2蛋白中删除这个三肽会导致过氧化物酶体柠檬酸合酶错误分选到线粒体中。这些实验表明，CIT2蛋白包含一个隐蔽的线粒体靶向信号。
