Wakasugi T, Hirose T, Horihata M, Tsudzuki T, Kössel H, Sugiura M
Center for Gene Research, Nagoya University, Japan.
Proc Natl Acad Sci U S A. 1996 Aug 6;93(16):8766-70. doi: 10.1073/pnas.93.16.8766.
The phenomenon of RNA editing has been found to occur in chloroplasts of several angiosperm plants. Comparative analysis of the entire nucleotide sequence of a gymnosperm [Pinus thunbergii (black pine)] chloroplast genome allowed us to predict several potential editing sites in its transcripts. Forty-nine such sites from 14 genes/ORFs were analyzed by sequencing both cDNAs from the transcripts and the corresponding chloroplast DNA regions, and 26 RNA editing sites were identified in the transcripts from 12 genes/ORFs, indicating that chloroplast RNA editing is not restricted to angiosperms but occurs in the gymnosperm, too. All the RNA editing events are C-to-U conversions; however, many new codon substitutions and creation of stop codons that have not so far been reported in angiosperm chloroplasts were observed. The most striking is that two editing events result in the creation of an initiation and a stop codon within a single transcript, leading to the formation of a new reading frame of 33 codons. The predicted product is highly homologous to that deduced from the ycf7 gene (ORF31), which is conserved in the chloroplast genomes of many other plant species.
人们发现RNA编辑现象发生在几种被子植物的叶绿体中。对裸子植物（黑松）叶绿体基因组的全核苷酸序列进行比较分析，使我们能够预测其转录本中的几个潜在编辑位点。通过对转录本的cDNA和相应的叶绿体DNA区域进行测序，分析了来自14个基因/开放阅读框（ORF）的49个此类位点，在来自12个基因/ORF的转录本中鉴定出26个RNA编辑位点，这表明叶绿体RNA编辑并不局限于被子植物，在裸子植物中也会发生。所有的RNA编辑事件都是C到U的转换；然而，观察到许多新的密码子替换以及在被子植物叶绿体中尚未报道过的终止密码子的产生。最引人注目的是，两个编辑事件导致在单个转录本中产生一个起始密码子和一个终止密码子，从而形成一个由33个密码子组成的新阅读框。预测产物与从ycf7基因（ORF31）推导的产物高度同源，ycf7基因在许多其他植物物种的叶绿体基因组中是保守的。
