Gal S, Raikhel N V
MSU-DOE Plant Research Laboratory, East Lansing, MI 48824-1312.
Plant J. 1994 Aug;6(2):235-40. doi: 10.1046/j.1365-313x.1994.6020235.x.
Three different classes of signals for plant vacuolar targeting have been defined. Previous work has demonstrated that the carboxyl-terminal propeptide (CTPP) of barley lectin (BL) is a vacuolar targeting signal in tobacco plants. When a mutant BL protein lacking the CTPP is expressed in tobacco, the protein is secreted. In an effort to determine the universality of this signal, the CTPP was tested for its ability to target proteins to the vacuole of Saccharomyces cerevisiae. Genes encoding fusion proteins between the yeast secreted protein invertase and BL domains were synthesized and transformed into an invertase deletion mutant of yeast. Invertase assays on intact and detergent-solubilized cells demonstrated that invertase+CTPP was secreted, while nearly 90% of the invertase::BL+CTPP (fusion protein between invertase and BL containing the CTPP) and invertase::BL-CTPP proteins (fusion between invertase and BL lacking the CTPP) were retained intracellularly. These fusions were secreted in a mutant of yeast that normally secretes proteins targeted to the vacuole. With this and previous work, proteins representing all three classes of plant vacuolar targeting signals have now been tested in yeast, and in all cases, the experiments indicate that the plant proteins are directed to the yeast vacuole using signals other than those recognized by plants.
现已确定了三类不同的植物液泡靶向信号。先前的研究表明，大麦凝集素（BL）的羧基末端前肽（CTPP）是烟草植物中的一种液泡靶向信号。当在烟草中表达缺乏CTPP的突变型BL蛋白时，该蛋白会被分泌。为了确定这种信号的通用性，测试了CTPP将蛋白质靶向酿酒酵母液泡的能力。合成了编码酵母分泌蛋白转化酶与BL结构域之间融合蛋白的基因，并将其转化到酵母的转化酶缺失突变体中。对完整细胞和经去污剂溶解的细胞进行的转化酶测定表明，转化酶+CTPP被分泌，而近90%的转化酶::BL+CTPP（转化酶与含有CTPP的BL之间的融合蛋白）和转化酶::BL-CTPP蛋白（转化酶与缺乏CTPP的BL之间的融合蛋白）被保留在细胞内。这些融合蛋白在一个通常分泌靶向液泡的蛋白质的酵母突变体中被分泌。结合这项研究和先前的工作，现已在酵母中测试了代表所有三类植物液泡靶向信号的蛋白质，在所有情况下，实验表明植物蛋白是利用植物无法识别的信号被导向酵母液泡的。
