Klinkert Birgit, Schwarz Christian, Pohlmann Stephan, Pierre Yves, Girard-Bascou Jacqueline, Nickelsen Jörg
Allgemeine und Molekulare Botanik, Ruhr-Universität Bochum, Universitätsstr. 150, 44780 Bochum, Germany.
Mol Genet Genomics. 2005 Dec;274(6):637-43. doi: 10.1007/s00438-005-0056-x. Epub 2005 Oct 22.
The photosynthetic chloroplast mutant G64 of Chlamydomonas reinhardtii was shown to contain a single point mutation within the 5' region of the psbD gene encoding the D2 protein of the photosystem II reaction center. The mutation affects the sequence element TATAATAT which has previously been hypothesized to function as the psbD promoter. Run-on analysis confirmed that transcription of psbD in the mutant was reduced to approximately 10% of the wild-type level. However, psbD mRNA accumulated to approximately 35%, despite the prominent decrease in RNA synthesis. This suggests that RNA-stabilization effects can compensate to some extent for a reduction in transcriptional activity. Interestingly, a direct correlation between transcript levels and the accumulation of the psbD gene product, the D2-protein, was observed in G64. The data suggest that posttranscriptionally acting regulatory factors determine the rate-limiting steps of chloroplast psbD gene expression.
莱茵衣藻的光合叶绿体突变体G64被证明在编码光系统II反应中心D2蛋白的psbD基因的5'区域内存在一个单点突变。该突变影响了序列元件TATAATAT，此前曾假设该元件作为psbD启动子发挥作用。连续分析证实，突变体中psbD的转录降至野生型水平的约10%。然而，尽管RNA合成显著减少，psbD mRNA仍积累至约35%。这表明RNA稳定效应可以在一定程度上补偿转录活性的降低。有趣的是，在G64中观察到转录本水平与psbD基因产物D2蛋白的积累之间存在直接相关性。数据表明，转录后起作用的调节因子决定了叶绿体psbD基因表达的限速步骤。
