Voelker R, Barkan A
Institute of Molecular Biology, University of Oregon, Eugene 97403, USA.
Mol Gen Genet. 1995 Dec 15;249(5):507-14. doi: 10.1007/BF00290576.
Nuclear genes essential for the biogenesis of the chloroplast cytochrome b6f complex were identified by mutations that cause the specific loss of the complex. We describe four transposon-induced maize mutants that lack cytochrome b6f proteins but contain normal levels of other photosynthetic complexes. The four mutations define two nuclear genes. To identify the step at which each mutation blocks protein accumulation, mRNAs encoding each subunit were examined by Northern hybridization analysis and the rates of subunit synthesis were examined in pulse-labeling experiments. In each mutant the mRNAs encoding the known subunits of the complex were normal in size and abundance and the major subunits were synthesized at normal rates. Thus, these mutations block the biogenesis of the cytochrome b6f complex at a post-translational step. The two nuclear genes identified by these mutations may encode previously unknown subunits, be involved in prosthetic group synthesis or attachment, or facilitate assembly of the complex. These mutations were also used to provide evidence for the authenticity of a proposed fifth subunit of the complex and to demonstrate a role for the cytochrome b6f complex in protecting photosystem II from light-induced degradation.
通过导致叶绿体细胞色素b6f复合体特异性缺失的突变，鉴定出了对该复合体生物合成至关重要的核基因。我们描述了四个转座子诱导的玉米突变体，它们缺乏细胞色素b6f蛋白，但其他光合复合体的水平正常。这四个突变定义了两个核基因。为了确定每个突变阻断蛋白质积累的步骤，通过Northern杂交分析检测了编码每个亚基的mRNA，并在脉冲标记实验中检测了亚基合成速率。在每个突变体中，编码该复合体已知亚基的mRNA大小和丰度正常，主要亚基以正常速率合成。因此，这些突变在翻译后步骤阻断了细胞色素b6f复合体的生物合成。这些突变鉴定出的两个核基因可能编码以前未知的亚基，参与辅基合成或附着，或促进复合体的组装。这些突变还被用于为该复合体提议的第五个亚基的真实性提供证据，并证明细胞色素b6f复合体在保护光系统II免受光诱导降解方面的作用。
