Karpinska B, Karpinski S, Hällgren J
Department of Forest Genetics and Plant Physiology, Faculty of Forestry, Swedish University of Agricultural Sciences, S-90183 Umeâ, Sweden.
Curr Genet. 1997 Apr;31(4):343-7. doi: 10.1007/s002940050214.
ChlB is one of three chloroplast genes shown so far to be required for light-independent chlorophyll synthesis. It occurs in some algae, lower plants, and gymnosperms, but not in angiosperms. We have demonstrated, for the first time in conifer chloroplasts, the presence of two internal C to U editing sites in this transcript. In the chlB transcript of Pinus sylvestris, the editing of the second position in a CCG codon leads to an amino-acid substitution from proline to leucine. Editing of a nearby CGG codon, resulting in an arginine to tryptophan substitution, has also been observed. The nucleotide sequence of this region has been compared with other species of gymnosperms. Out of seven species analysed, editing at both sites has only been detected in spruce, while in Larix only the editing which results in the Arg to Trp substitution was found. In other cases, both leucine and tryptophan are encoded by cpDNA, suggesting that conservation of these amino acids, through encoding by DNA or by editing of the RNA, is critical for the protein function. Transcripts are partially edited at the CGG codon and the relative abundance of cDNA molecules with the edited C is species-specific. The possible involvement of RNA editing in the regulation of gene expression in different organs of pine seedlings is discussed.
ChlB是迄今为止已表明的光独立叶绿素合成所需的三个叶绿体基因之一。它存在于一些藻类、低等植物和裸子植物中，但不存在于被子植物中。我们首次在针叶树叶绿体中证明了该转录本中存在两个内部C到U的编辑位点。在欧洲赤松的chlB转录本中，CCG密码子第二位的编辑导致脯氨酸到亮氨酸的氨基酸替换。还观察到附近的CGG密码子的编辑，导致精氨酸到色氨酸的替换。该区域的核苷酸序列已与其他裸子植物物种进行了比较。在分析的七个物种中，仅在云杉中检测到两个位点的编辑，而在落叶松中仅发现导致精氨酸到色氨酸替换的编辑。在其他情况下，亮氨酸和色氨酸均由叶绿体DNA编码，这表明通过DNA编码或RNA编辑来保守这些氨基酸对于蛋白质功能至关重要。转录本在CGG密码子处部分编辑，具有编辑后C的cDNA分子的相对丰度具有物种特异性。讨论了RNA编辑可能参与调控松树幼苗不同器官中的基因表达。
