Transposon-disruption of a maize nuclear gene, tha1, encoding a chloroplast SecA homologue: in vivo role of cp-SecA in thylakoid protein targeting.
Transposon-disruption of a maize nuclear gene, tha1, encoding a chloroplast SecA homologue: in vivo role of cp-SecA in thylakoid protein targeting.
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发表时间：
1997-02
期刊：
影响因子：
3.3
通讯作者：
R. Voelker;J. Mendel-Hartvig;A. Barkan
中科院分区：
文献类型：
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作者：
R. Voelker;J. Mendel-Hartvig;A. Barkan
玉米的一个核突变体tha1，在跨类囊体膜的蛋白质运输方面表现出缺陷，以前曾被描述过。在tha1基因座插入转座子有助于部分tha1基因的克隆。与细菌、豌豆和菠菜的secA基因有很强的序列相似性，表明tha1编码一个secA同源物(cp-secA)。Tha1-ref等位基因要么为零，要么几乎为空，因为在突变的叶片中检测不到tha1mRNA，cp-SecA的积累减少了40倍。这些结果与前面描述的突变表型相结合，表明cp-SecA在体内起到促进OEC33、PSI-F和PLASTIONIN转位的作用，但对OEC23和OEC16的转位没有作用。我们的结果证实了根据体外实验结果对cp-SecA功能的预测，并建立了cp-SecA的几个新功能，包括靶向叶绿体编码的蛋白质细胞色素f，以及靶向黄体中的蛋白质，黄体是一种非光合作用的质体类型。我们的发现是，尽管几乎或完全没有cp-SecA，适当靶向的叶绿体蛋白和细胞色素f在类囊体膜上的积累仅减少了几倍，这表明cp-SecA促进了它们在体内的跨膜转运，但不是必需的。
A nuclear mutant of maize, tha1, which exhibited defects in the translocation of proteins across the thylakoid membrane, was described previously. A transposon insertion at the tha1 locus facilitated the cloning of portions of the tha1 gene. Strong sequence similarity with secA genes from bacteria, pea and spinach indicates that tha1 encodes a SecA homologue (cp-SecA). The tha1-ref allele is either null or nearly so, in that tha1 mRNA is undetectable in mutant leaves and cp-SecA accumulation is reduced > or = 40-fold. These results, in conjunction with the mutant phenotype described previously, demonstrate that cp-SecA functions in vivo to facilitate the translocation of OEC33, PSI-F and plastocyanin but does not function in the translocation of OEC23 and OEC16. Our results confirm predictions for cp-SecA function made from the results of in vitro experiments and establish several new functions for cp-SecA, including roles in the targeting of a chloroplast-encoded protein, cytochrome f, and in protein targeting in the etioplast, a nonphotosynthetic plastid type. Our finding that the accumulation of properly targeted plastocyanin and cytochrome f in tha1-ref thylakoid membranes is reduced only a few-fold despite the near or complete absence of cp-SecA suggests that cp-SecA facilitates but is not essential in vivo for their translocation across the membrane.