Cushman J C, Hallick R B, Price C A
Waksman Institute of Microbiology, Rutgers University, Piscataway, NJ 08854.
Curr Genet. 1988 Feb;13(2):159-71. doi: 10.1007/BF00365651.
We have determined the complete nucleotide sequence of the two genes encoding the P700 chlorophyll a apoproteins of the photosystem I reaction center of the Euglena gracilis chloroplast genome. The two genes are separated by 77 bp, are of the same polarity, and span a region which is greater than 9.0 kbp. The psaA gene (751 codons) is interrupted by three introns and the psaB gene (734 codons) by six introns. The introns range in size from 361 to 590 bp, whereas the exons range in size from 42 to 1,194 bp. The introns are extremely AT rich with a pronounced base bias of T greater than A greater than G greater than C in the RNA-like strand. Like other interrupted protein genes in the Euglena chloroplast genome, the psaA and psaB introns are similar to mitochondrial group II introns in having the splice junction consensus sequence, 5' GTGCGNTTCG ..... INTRON ..... TTAATTTTAT 3' and conserved secondary structural features. Except for the placement of the first intron, the intron-exon organization of these two highly homologous genes is not conserved. The other introns fall at or near putative surface domains of the predicted gene products. The psaA and psaB gene products are 74% homologous to one another and 93% and 95% homologous, respectively, to the psaA and psaB gene products of higher plant chloroplasts. The predicted secondary structure derived from the primary amino acid sequence has 11 potential membrane-spanning domains.
我们已经确定了编码纤细裸藻叶绿体基因组光系统I反应中心P700叶绿素a脱辅基蛋白的两个基因的完整核苷酸序列。这两个基因被77个碱基对隔开，极性相同，跨度大于9.0千碱基对。psaA基因（751个密码子）被3个内含子中断，psaB基因（734个密码子）被6个内含子中断。内含子大小在361至590个碱基对之间，而外显子大小在42至1194个碱基对之间。内含子富含AT，在RNA样链中碱基偏向明显为T＞A＞G＞C。与纤细裸藻叶绿体基因组中其他中断的蛋白质基因一样，psaA和psaB内含子与线粒体II类内含子相似，具有剪接连接共有序列5' GTGCGNTTCG ..... 内含子 ..... TTAATTTTAT 3'和保守的二级结构特征。除了第一个内含子的位置外，这两个高度同源基因的内含子-外显子组织并不保守。其他内含子位于预测基因产物的假定表面结构域处或附近。psaA和psaB基因产物彼此同源性为74%，分别与高等植物叶绿体的psaA和psaB基因产物同源性为93%和95%。从一级氨基酸序列推导的预测二级结构有11个潜在的跨膜结构域。
