Tingey S V, Tsai F Y, Edwards J W, Walker E L, Coruzzi G M
Laboratory of Plant Molecular Biology, Rockefeller University, New York, New York 10021-6399.
J Biol Chem. 1988 Jul 15;263(20):9651-7.
We have shown that the individual members of the plant gene family for glutamine synthetase (GS) are differentially expressed in vivo, and each encode distinct GS polypeptides which are targeted to different subcellular compartments (chloroplast or cytosol). At the polypeptide level, chloroplast GS (GS2) and cytosolic GS (GS1 and GSn) are distinct and show an organ-specific distribution. We have characterized full length cDNA clones encoding chloroplast or cytosolic GS of pea. In vitro translation products encoded by three different GS cDNA clones, correspond to the mature GS2, GS1, and GSn polypeptides present in vivo. pGS185 encodes a precursor to the chloroplast GS2 polypeptide as shown by in vitro chloroplast uptake experiments. The pGS185 translation product is imported into the chloroplast stroma and processed to a polypeptide which corresponds in size and charge to that of mature chloroplast stromal GS2 (44 kDa). The 49 amino terminal amino acids encoded by pGS185 are designated as a chloroplast transit peptide by functionality in vitro, and amino acid homology to other transit peptides. The cytosolic forms of GS (GS1 and GSn) are encoded by highly homologous but distinct mRNAs. pGS299 encodes the cytosolic GS1 polypeptide (38 kDa), while pGS341 (Tingey, S. V., Walker, E. L., and Coruzzi, G. M. (1987) EMBO. J. 6, 1-9) encodes a cytosolic GSn polypeptide (37 kDa). The homologous nuclear genes for chloroplast and cytosolic GS show different patterns of expression in vivo. GS2 expression in leaves is modulated by light, at the level of steady state mRNA and protein, while the expression of cytosolic GS is unaffected by light. The light-induced expression of GS2 is due at least in part to a phytochrome mediated response. Nucleotide sequence analysis indicates that chloroplast and cytosolic GS have evolved from a common ancestor and suggest a molecular mechanism for chloroplast evolution.
我们已经证明，植物谷氨酰胺合成酶（GS）基因家族的各个成员在体内差异表达，并且每个成员编码不同的GS多肽，这些多肽靶向不同的亚细胞区室（叶绿体或细胞质）。在多肽水平上，叶绿体GS（GS2）和细胞质GS（GS1和GSn）是不同的，并且呈现出器官特异性分布。我们已经鉴定了编码豌豆叶绿体或细胞质GS的全长cDNA克隆。由三个不同的GS cDNA克隆编码的体外翻译产物，对应于体内存在的成熟GS2、GS1和GSn多肽。如体外叶绿体摄取实验所示，pGS185编码叶绿体GS2多肽的前体。pGS185翻译产物被导入叶绿体基质，并加工成一种多肽，其大小和电荷与成熟叶绿体基质GS2（44 kDa）的多肽相对应。pGS185编码的49个氨基末端氨基酸通过体外功能以及与其他转运肽的氨基酸同源性被指定为叶绿体转运肽。GS的细胞质形式（GS1和GSn）由高度同源但不同的mRNA编码。pGS299编码细胞质GS1多肽（38 kDa），而pGS341（廷吉，S. V.，沃克，E. L.，和科鲁齐，G. M.（1987年）《欧洲分子生物学组织杂志》6，1 - 9）编码细胞质GSn多肽（37 kDa）。叶绿体和细胞质GS的同源核基因在体内表现出不同的表达模式。叶片中GS2的表达在稳态mRNA和蛋白质水平上受光调节，而细胞质GS的表达不受光影响。GS2的光诱导表达至少部分归因于一种光敏色素介导的反应。核苷酸序列分析表明，叶绿体和细胞质GS起源于一个共同的祖先，并提出了叶绿体进化的分子机制。
