Creissen G, Reynolds H, Xue Y, Mullineaux P
John Innes Centre, Norwich Research Park, Colney, Norwich, UK.
Plant J. 1995 Aug;8(2):167-75. doi: 10.1046/j.1365-313x.1995.08020167.x.
N-terminal presequences from cDNAs encoding mitochondrion- or chloroplast-specific proteins are able, with variable efficiencies, to target preproteins to their respective organelles. In the few cases studied in which a nuclear-encoded protein is found in both these organelles, each compartment-specific isoform is encoded by a separate gene. Glutathione reductase (GR) from peas is encoded by a single nuclear gene and yet GR is distributed between chloroplasts, mitochondria and the cytosol. Previous sequence analysis of a full-length GR cDNA revealed the presence of a putative plastid transit peptide. However, expression of this cDNA in transgenic tobacco resulted in substantially elevated GR activities in both chloroplasts and mitochondria in four independent lines examined. There was no effect on expression of the endogenous tobacco GR genes. Replacement of the GR presequence with presequences from pea rbcS (chloroplast) and Nicotiana plumbaginifolia Mn-SOD (mitochondrion) resulted in targeting of GR only into the appropriate organelle. Expression of a fusion protein between the amino terminal region of GR and phosphinothricin acetyl transferase resulted in targeting of the foreign protein to chloroplasts and mitochondria. Thus, the pea GR presequence is capable of co-targeting this enzyme or a foreign protein to chloroplasts and mitochondria in vivo. This is the first example of co-targeting by a higher plant preprotein.
编码线粒体或叶绿体特异性蛋白的cDNA的N端前序列能够以不同效率将前体蛋白靶向到各自的细胞器。在少数已研究的案例中，若在这两种细胞器中都发现了核编码蛋白，则每个特定于细胞器的同工型都由一个单独的基因编码。豌豆中的谷胱甘肽还原酶（GR）由单个核基因编码，但GR却分布在叶绿体、线粒体和细胞质中。此前对全长GR cDNA的序列分析揭示了一个推定的质体转运肽的存在。然而，在四个独立检测的转基因烟草株系中，该cDNA的表达使得叶绿体和线粒体中的GR活性均大幅升高。这对烟草内源性GR基因的表达没有影响。用豌豆rbcS（叶绿体）和烟草垂花烟草锰超氧化物歧化酶（线粒体）的前序列替换GR前序列，结果导致GR仅靶向到相应的细胞器中。GR氨基端区域与膦丝菌素乙酰转移酶之间的融合蛋白的表达导致外源蛋白靶向到叶绿体和线粒体中。因此，豌豆GR前序列能够在体内将这种酶或外源蛋白共同靶向到叶绿体和线粒体中。这是高等植物前体蛋白共同靶向的首个例子。
