Christopher D A, Cushman J C, Price C A, Hallick R B
Department of Molecular and Cellular Biology, University of Arizona, Tucson 85721.
Curr Genet. 1988 Sep;14(3):275-85. doi: 10.1007/BF00376748.
The nucleotide sequence (4,814 bp) was determined for a cluster of five ribosomal protein genes and their DNA flanking regions from the chloroplast genome of Euglena gracilis. The genes are organized as rpl23-150 bp spacer-rpl2-59 bp spacer-rps19-110 bp spacer-rpl22-630 bp spacer-rps3. The genes are all of the same polarity and reside 148 bp downstream from an operon for two genes of photosystem I and four genes of photosystem II. The Euglena ribosomal protein gene cluster resembles the S-10 ribosomal protein operon of Escherichia coli in gene organization and follows the exact linear order of the analogous genes in the tobacco and liverwort chloroplast genomes. The number and positions of introns in the Euglena ribosomal protein loci are different from their higher plant counterparts. The Euglena rpl23, rps19 and rps3 loci are unique in that they contain three, two and two introns, respectively, whereas rpl2 and rpl22 lack introns. The introns found in rpl23 (106, 99 and 103 bp), rps19 (103 and 97 bp) and rps3 intron 2 (102 bp) appear to represent either a new class of chloroplast intron found only in constitutively expressed genes, or possibly a degenerate version of Euglena chloroplast group II introns. They are deficient in bases C and G and extremely rich in base T, with a base composition of 53-76% T, 25-34% A, 3-10% G and 2-7% C in the mRNA-like strand. These six introns show minimal resemblance to group II chloroplast introns. They have a degenerate version of the group II intron conserved boundary sequences at their 5' and 3' ends. No conserved internal secondary structures are apparent. By contrast, rps3 intron 1 (409 bp) has a potential group II core secondary structure. The five genes, rpl23 (101 codons), rpl2 (278 codons), rps19 (95 codons), rpl22 (114 codons) and rps3 (220 codons) encode lysine-rich polypeptides with predicted molecular weights of 12,152, 31,029, 10,880, 12,819, and 25,238, respectively. The Euglena gene products are 18-50%, and 29-58% identical in primary structure to their E. coli and higher plant counterparts, respectively. Oligonucleotide sequences corresponding to Euglena chloroplast ribosome binding sites are not apparent in the intergenic regions. Inverted repeat sequences are found in the upstream flanking region of rpl23 and downstream from rps3.
测定了纤细裸藻叶绿体基因组中一组五个核糖体蛋白基因及其DNA侧翼区域的核苷酸序列（4814 bp）。这些基因的排列方式为：rpl23 - 150 bp间隔区 - rpl2 - 59 bp间隔区 - rps19 - 110 bp间隔区 - rpl22 - 630 bp间隔区 - rps3。这些基因具有相同的极性，位于光系统I的两个基因和光系统II的四个基因组成的操纵子下游148 bp处。裸藻核糖体蛋白基因簇在基因组织上类似于大肠杆菌的S - 10核糖体蛋白操纵子，并且遵循烟草和地钱叶绿体基因组中类似基因的确切线性顺序。裸藻核糖体蛋白基因座中内含子的数量和位置与高等植物的不同。裸藻的rpl23、rps19和rps3基因座分别含有三个、两个和两个内含子，而rpl2和rpl22没有内含子。在rpl23（106、99和103 bp）、rps19（103和97 bp）和rps3内含子2（102 bp）中发现的内含子似乎代表了仅在组成型表达基因中发现的一类新的叶绿体内含子，或者可能是裸藻叶绿体II类内含子的退化版本。它们缺乏碱基C和G，而碱基T极其丰富，在类mRNA链中的碱基组成为53 - 76% T、25 - 34% A、3 - 10% G和2 - 7% C。这六个内含子与II类叶绿体内含子的相似性极小。它们在5'和3'末端具有II类内含子保守边界序列的退化版本。没有明显的保守内部二级结构。相比之下，rps3内含子1（409 bp）具有潜在的II类核心二级结构。五个基因，rpl23（101个密码子）、rpl2（278个密码子）、rps19（95个密码子）、rpl22（114个密码子）和rps3（220个密码子）分别编码富含赖氨酸的多肽，预测分子量分别为12,152、31,029、10,880、12,819和25,238。裸藻基因产物在一级结构上与大肠杆菌和高等植物对应物的同一性分别为18 - 50%和29 - 58%。在基因间隔区没有明显对应于裸藻叶绿体核糖体结合位点的寡核苷酸序列。在rpl23的上游侧翼区域和rps3的下游发现了反向重复序列。
