Liaud M F, Valentin C, Brandt U, Bouget F Y, Kloareg B, Cerff R
Institut für Genetik, Universität Braunschweig, Germany.
Plant Mol Biol. 1993 Dec;23(5):981-94. doi: 10.1007/BF00021813.
Our previous phylogenetic analysis based on cDNA sequences of chloroplast and cytosolic glyceraldehyde-3-phosphate dehydrogenases (GAPDH; genes GapA and GapC, respectively) of the red alga Chondrus crispus suggested that rhodophytes and green plants are sister groups with respect to plastids and mitochondria and diverged at about the same time or somewhat later than animals and fungi. Here we characterize the genomic sequences of genes GapC and GapA of C. crispus with respect to promotor structures, intron/exon organization, genomic complexity, G + C content, CpG suppression and their transcript levels in gametophytes and protoplasts, respectively. To our knowledge this is the first report on nuclear protein genes of red algae. The GapC gene is G + C-rich, contains no introns and displays a number of classic sequence motifs within its promotor region, such as TATA, CAAT, GC boxes and several elements resembling the plant-specific G-box palindrome. The GapA gene has a moderate G+C content, a single CAAT box motif in its promotor region and a single intron of 115 bp near its 5' end. This intron occupies a conserved position corresponding to that of intron 1 in the transit peptide region of chloroplast GAPDH genes (GapA and GapB) of higher plants. It has consensus sequences similar to those of yeast introns and folds into a conspicuous secondary structure of -61.3 kJ. CpG profiles of genes GapC and GapA and their flanking sequences show no significant CpG depletion suggesting that these genomic sequences are not methylated. Genomic Southern blots hybridized with generic and gene specific probes indicate that both genes are encoded by single loci composed of multiple polymorphic alleles. Northern hybridizations demonstrate that both genes are expressed in gametophytes but not in protoplasts where appreciable amounts of transcripts can only be detected for GapC.
我们之前基于红藻皱波角叉菜叶绿体和胞质甘油醛-3-磷酸脱氢酶（GAPDH；分别为基因GapA和GapC）的cDNA序列进行的系统发育分析表明，就质体和线粒体而言，红藻和绿色植物是姐妹类群，它们大约在同一时间或略晚于动物和真菌分化。在此，我们分别从启动子结构、内含子/外显子组织、基因组复杂性、G + C含量、CpG抑制及其在配子体和原生质体中的转录水平等方面，对皱波角叉菜基因GapC和GapA的基因组序列进行了表征。据我们所知，这是关于红藻核蛋白基因的首次报道。GapC基因富含G + C，不含内含子，在其启动子区域显示出许多经典的序列基序，如TATA、CAAT、GC框以及几个类似于植物特异性G-box回文的元件。GapA基因的G + C含量适中，其启动子区域有一个单一的CAAT框基序，在其5'端附近有一个115 bp的单一内含子。这个内含子占据的保守位置与高等植物叶绿体GAPDH基因（GapA和GapB）转运肽区域的内含子1相对应。它具有与酵母内含子相似的共有序列，并折叠成一个显著的二级结构，能量为-61.3 kJ。基因GapC和GapA及其侧翼序列的CpG图谱显示没有明显的CpG缺失，表明这些基因组序列没有甲基化。与通用探针和基因特异性探针杂交的基因组Southern印迹表明，这两个基因均由由多个多态性等位基因组成的单一位点编码。Northern杂交表明，这两个基因在配子体中表达，但在原生质体中不表达，在原生质体中只能检测到GapC有可观数量的转录本。
