Lehrstuhl für Allgemeine Botanik, Ruhr-Universität Bochum, Postfach 10 21 48, D-4630 Bochum 1, FRG.
EMBO J. 1987 Aug;6(8):2185-95. doi: 10.1002/j.1460-2075.1987.tb02489.x.
The two homologous genes for the P700 chlorophyll a-apoproteins (ps1A1 and ps1A2) are encoded by the plastom in the green alga Chlamydomonas reinhardii. The structure and organization of the two genes were determined by comparison with the homologous genes from maize using data from heterologous hybridizations as well as from DNA and RNA sequencing. While the ps1A2 (736 codons) gene shows a continuous gene organization, the ps1A1 (754 codons) gene possesses some unusual features. The discontinuous gene is split into three separate exons which are scattered around the circular chloroplast genome. Exon 1 (86 bp) is separated by approximately 50 kb from exon 2 (198 bp), which is located approximately 90 kb apart from exon 3 (1984 bp). All exons are flanked by intronic sequences of group II. Transcription analysis reveals that the ps1A2 gene hybridizes with a 2.8-kb transcript, while all exon regions of the ps1A1 gene are homologous to a mature mRNA of 2.7 kb. From our data we conclude that the three distantly separated exonic sequences of the ps1A1 gene constitute a functional gene which probably operates by a trans-splicing mechanism.
两个同源的 P700 叶绿素 a 脱辅基蛋白（ps1A1 和 ps1A2）基因由绿藻衣藻的质体编码。通过与玉米的同源基因进行比较，利用异源杂交以及 DNA 和 RNA 测序的数据，确定了这两个基因的结构和组织。虽然 ps1A2（736 个密码子）基因显示出连续的基因组织，但 ps1A1（754 个密码子）基因具有一些不寻常的特征。不连续基因分为三个独立的外显子，散布在圆形叶绿体基因组周围。外显子 1（86 个碱基对）与外显子 2（198 个碱基对）之间相隔约 50kb，外显子 2 与外显子 3（1984 个碱基对）相隔约 90kb。所有外显子都被 II 组内含子序列包围。转录分析显示 ps1A2 基因与 2.8kb 的转录物杂交，而 ps1A1 基因的所有外显子区域都与成熟的 2.7kb mRNA 同源。根据我们的数据，我们得出结论，ps1A1 基因的三个远隔的外显子序列构成了一个功能基因，它可能通过反式剪接机制发挥作用。
