New chloroplast genes involved in assembly of photosystem 1 complex.

光系统1驱动光诱导的电子转移反应，由十多个亚基和一百多个辅因子组成。这种复合体的生物发生需要这些成分的协同组装。在本研究中，我们对绿藻Chiamomonas rehardtii的叶绿体基因ycf3和ycf4进行了鉴定。利用生物转化，ycf4或被叶绿体可选择标记盒干扰。缺乏ycf4或ycf3的转化子不能光自养生长，光系统I活性不足。Western印迹分析表明，光系统I(PSI)复合体在这些转化子的类囊体膜中不稳定积累。Ycf4和Ycf3定位于类囊体膜上，但不稳定地与PSI复合体结合，在缺乏PSI的突变体中积累到野生型水平。RNA印迹杂交表明，psaA、psaB和PsaC的转录在这些突变体中正常积累，嵌合报告基因的使用表明Ycf3不是启动psaA和psaB mRNAs翻译所必需的。我们的结果表明，Ycf3和Ycf4是PSI复合体稳定积累所必需的。

The photosystem 1 drives light-induced electron transfer reaction from plastocyanin to ferredoxin and consists of more than ten subunits and over one hundred cofactors. The biogenesis of this complex requires cooperative assembly of these components.In the present study, the chloroplast genes ycf3 and ycf4 from the green alga Chiamydomonas reinhardtii have been characterized. Using biolistic transformation, ycf4 or were disrupted with a chioroplast selectable marker cassette. Transformants lacking ycf4 or ycf3 were unable to grow photoautotrophically and were deficient in photosystem I activity. Western blot analysis showed that the photosystem I (PSI) complex does not accumulate stably in thylakoid membranes of these transformants. Ycf4 and Ycf3 were localized on thylakoid membranes but not stably associated with the PSI complex and accumulated to wild type levels in mutants lacking PSI.RNA blot hybridizations showed that transcripts of psaA, psaB and psaC accumulate normally in these mutants and use of chimeric reporter genes revealed that Ycf3 is not required for initiation of translation of psaA and psaB mRNA.Our results indicate that Ycf3 and Ycf4 are required for stable accumulation of the PSI complex.