Nakrieko Kerry-Ann, Mould Ruth M, Smith Alison G
Department of Plant Sciences, University of Cambridge, UK.
Eur J Biochem. 2004 Feb;271(3):509-16. doi: 10.1046/j.1432-1033.2003.03950.x.
Phosphorylation of the transit peptide of several chloroplast-targeted proteins enables the binding of 14-3-3 proteins. The complex that forms, together with Hsp70, has been demonstrated to be an intermediate in the chloroplast protein import pathway in vitro[May, T. & Soll, J. (2000) Plant Cell 12, 53-63]. In this paper we report that mutagenesis (in order to remove the phosphorylation site) of the transit peptide of the small subunit of ribulose bisphosphate carboxylase/oxygenase did not affect its ability to target green fluorescent protein to chloroplasts in vivo. We also found no mistargeting to other organelles such as mitochondria. Similar alterations to the transit peptides of histidyl- or cysteinyl-tRNA synthetase, which are dual-targeted to chloroplasts and mitochondria, had no effect on their ability to target green fluorescent protein in vivo. Thus, phosphorylation of the transit peptide is not responsible for the specificity of chloroplast import.
几种叶绿体靶向蛋白的转运肽磷酸化能够使14-3-3蛋白结合。已证明形成的复合物与热休克蛋白70（Hsp70）一起，在体外是叶绿体蛋白导入途径中的一个中间体[梅，T.和索尔，J.（2000年）《植物细胞》12卷，53 - 63页]。在本文中我们报告，对1,5 - 二磷酸核酮糖羧化酶/加氧酶小亚基的转运肽进行诱变（以去除磷酸化位点），并不影响其在体内将绿色荧光蛋白靶向叶绿体的能力。我们也未发现其错误靶向至其他细胞器如线粒体的情况。对组氨酰 - 或半胱氨酰 - tRNA合成酶的转运肽进行类似改变，这些酶可双靶向至叶绿体和线粒体，对它们在体内将绿色荧光蛋白靶向的能力也没有影响。因此，转运肽的磷酸化并不负责叶绿体导入的特异性。
