New chloroplast genes involved in assembly of photosystem 1 complex.

光系统1由十多个亚基和一百多个辅因子组成，负责光诱导的质体蓝蛋白到铁氧还蛋白的电子传递反应。本研究对来自绿色莱氏奇异果（Chiamyamyeleinhardtii）的叶绿体基因ycf 3和ycf 4进行了鉴定。使用生物射弹转化，用叶绿体选择标记盒破坏ycf 4或ycf 4。缺乏ycf 4或ycf 3的转化体不能生长光自养，缺乏光系统I活性。Western印迹分析表明，光系统I（PSI）复合物不稳定积累在这些转化体的类囊体膜。Ycf 4和Ycf 3定位于类囊体膜上，但不稳定地与PSI复合物结合，并且在缺乏PSI的突变体中积累至野生型水平。psaB和psaC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psaA和psaB mRNA翻译起始所必需的。PSI复合物的稳定积累。

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.