Sugiura M
Center for Gene Research, Nagoya University, Japan.
Essays Biochem. 1995;30:49-57.
The chloroplast genome consists of homogeneous circular DNA molecules. To date, the entire nucleotide sequences (120-190 kbp) of chloroplast genomes have been determined from eight plant species. The chloroplast genomes of land plants and green algae contain about 110 different genes, which can be classified into two main groups: genes involved in gene expression and those related to photosynthesis. The red alga Porphyra chloroplast genome has 70 additional genes, one-third of which are related to biosynthesis of amino acids and other low molecular mass compounds. Chloroplast genes contain at least three structurally distinct promoters and transcribe two or more classes of RNA polymerase. Two chloroplast genes, rps12 of land plants and psaA of Chlamydomonas, are divided into two to three pieces and scattered over the genome. Each portion is transcribed separately, and two to three separate transcripts are joined together to yield a functional mRNA by trans-splicing. RNA editing (C to U base changes) occurs in some of the chloroplast transcripts. Most edited codons are functionally significant, creating start and stop codons and changing codons to retain conserved amino acids.
叶绿体基因组由同源环状DNA分子组成。迄今为止，已测定了8种植物叶绿体基因组的完整核苷酸序列（120 - 190千碱基对）。陆地植物和绿藻的叶绿体基因组包含约110种不同的基因，可分为两大类：参与基因表达的基因和与光合作用相关的基因。红藻紫菜的叶绿体基因组有70个额外的基因，其中三分之一与氨基酸和其他低分子量化合物的生物合成有关。叶绿体基因至少包含三种结构不同的启动子，并转录两类或更多类的RNA聚合酶。陆地植物的rps12和衣藻的psaA这两个叶绿体基因被分成两到三段，分散在基因组中。每个部分分别转录，两到三个单独的转录本通过反式剪接连接在一起，产生功能性的mRNA。RNA编辑（C到U碱基变化）发生在一些叶绿体转录本中。大多数编辑后的密码子具有功能意义，可产生起始和终止密码子，并改变密码子以保留保守的氨基酸。
