Searching limiting steps in the expression of chloroplast-encoded proteins:: relations between gene copy number, transcription, transcript abundance and translation rate in the chloroplast of Chlamydomonas reinhardtii
Searching limiting steps in the expression of chloroplast-encoded proteins:: relations between gene copy number, transcription, transcript abundance and translation rate in the chloroplast of Chlamydomonas reinhardtii
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DOI：
10.1046/j.1365-313x.2002.01340.x
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发表时间：
2002-07-01
期刊：
影响因子：
7.2
通讯作者：
Wollman, FA
中科院分区：
文献类型：
--
作者：
Eberhard, S;Drapier, D;Wollman, FA
本文系统研究了在混合营养和光营养条件下生长的莱茵衣藻（Chlamydomonas reinhardtii）叶绿体基因组拷贝数、转录、转录丰度与光合蛋白合成之间的定量关系。在后一种情况下，叶绿体基因拷贝数较低，大多数叶绿体转录物的半衰期和积累水平显著降低，但蛋白质合成的相对速度保持不变。我们的研究表明，在大多数情况下，叶绿体蛋白合成对叶绿体中基因拷贝数或转录物丰度的变化不太敏感。用5-氟-2'-脱氧尿苷处理可以抑制叶绿体DNA复制并大大减少叶绿体基因组的拷贝数，但对大多数叶绿体转录物的丰度影响有限，对蛋白质合成速度几乎没有影响。当使用选择性抑制叶绿体转录的利福平时，我们发现叶绿体中剩余转录本的水平与叶绿体蛋白质合成速率之间没有直接相关性。对于两个叶绿体基因，转录量减少90%并不会导致相应蛋白产物的合成速率下降。总之，我们的研究结果表明，叶绿体中不存在基因剂量效应，转录物丰度不限制叶绿体编码蛋白的表达。
We performed a systematic investigation of the quantitative relationship between genome copy number, transcription, transcript abundance and synthesis of photosynthetic proteins in the chloroplast of the green algae Chlamydomonas reinhardtii grown either in mixotrophic or phototrophic conditions. The chloroplast gene copy number is lower in the latter condition and the half-life and accumulation levels of most chloroplast transcripts are significantly reduced, although the relative rates of protein synthesis remain similar. Our study shows that, in most instances, chloroplast protein synthesis is poorly sensitive to changes in gene copy number or transcript abundance in the chloroplast. Treatment with 5-fluoro-2'-deoxyuridine, that inhibits chloroplast DNA replication and decreases extensively the number of copies of the chloroplast genome, had limited effects on the abundance of most chloroplast transcripts and little if any effect on the rates of protein synthesis. When using rifampicin, that selectively inhibits chloroplast transcription, we found no direct correlation between the level of transcripts remaining in the chloroplast and the rates of chloroplast protein synthesis. For two chloroplast genes, a 90% decrease in the amount of transcript did not cause a drop in the rate of synthesis of the corresponding protein product. Overall, our results demonstrate that there is no gene dosage effect in the chloroplast and that transcript abundance is not limiting in the expression of chloroplast-encoded protein.