Vierling E, Nagao R T, DeRocher A E, Harris L M
Department of Biochemistry, University of Arizona, Tucson 85721.
EMBO J. 1988 Mar;7(3):575-81. doi: 10.1002/j.1460-2075.1988.tb02849.x.
We have isolated cDNA clones from soybean and pea that specify nuclear-encoded heat shock proteins (HSPs) which localize to chloroplasts. The mRNAs for these HSPs are undetectable at control temperatures, but increase approximately 150-fold during a 2-h heat shock. Hybridization-selection followed by in vitro translation demonstrates that these HSPs are synthesized as precursor proteins which are processed by the removal of 5-6.5 kd during import into isolated chloroplasts. The nucleotide sequence of the cDNAs shows the derived amino acid sequences of the mature pea and soybean proteins are 79% identical. While the predicted transit peptide encoded by the pea cDNA has some characteristics typical of transit sequences, including high Ser content, multiple basic residues and no acidic residues, it lacks two domains proposed to be important for import and maturation of other chloroplast proteins. The carboxy-terminal region of the chloroplast HSP has significant homology to cytoplasmic HSPs from soybean and other eukaryotes. We hypothesize that the chloroplast HSP shares a common structural and functional domain with low mol. wt HSPs which localize to other parts of the cell, and may have evolved from a nuclear gene.
我们已从大豆和豌豆中分离出cDNA克隆，这些克隆可编码定位于叶绿体的核编码热休克蛋白（HSP）。在对照温度下无法检测到这些HSP的mRNA，但在2小时热激过程中其含量增加约150倍。杂交筛选后进行体外翻译表明，这些HSP作为前体蛋白合成，在导入分离的叶绿体过程中通过去除5 - 6.5 kd进行加工。cDNA的核苷酸序列显示，成熟豌豆和大豆蛋白的推导氨基酸序列有79%相同。虽然豌豆cDNA编码的预测转运肽具有一些转运序列的典型特征，包括高丝氨酸含量、多个碱性残基且无酸性残基，但它缺少两个对其他叶绿体蛋白的导入和成熟很重要的结构域。叶绿体HSP的羧基末端区域与大豆和其他真核生物的细胞质HSP有显著同源性。我们推测叶绿体HSP与定位于细胞其他部位的低分子量HSP具有共同的结构和功能域，并且可能从一个核基因进化而来。
