Marquardt J, Wans S, Rhiel E, Randolf A, Krumbein W E
ICBM/Geomikrobiologie, Carl von Ossietzky Universität Oldenburg, Carl-von-Ossietzky-Str. 9-11, 26111, Oldenburg, Germany.
Gene. 2000 Sep 19;255(2):257-65. doi: 10.1016/s0378-1119(00)00332-2.
Genes for light-harvesting proteins (lhc genes) of higher plants are well examined. However, little is known about the corresponding genes of algae, although this knowledge might give valuable information about the evolution of photosynthetic antennae. In the case of rhodophytes only two cDNA sequences from a single organism, Porphyridium cruentum, have been published. Here we describe an additional sequence from another species, the thermo-acidophilic red alga Galdieria sulphuraria. For the first time also a genomic sequence for a red algal lhc gene is presented. From a cDNA library of G. sulphuraria we isolated a clone containing an open reading frame for a protein of 302 amino acids with a deduced molecular mass of 33.86kDa. It shares major structural features with eukaryotic light-harvesting polypeptides. A proposed cleavage site between transit peptide and mature protein gives rise to a transit peptide of 119 amino acids and a mature protein of 183 residues. Hydropathy analysis suggests that the mature protein consists of three transmembrane helices. Several amino acid residues supposed to bind chlorophyll a and chlorophyll b in higher plants are conserved. The protein shows up to 69% identity and 81% similarity to the Porphyridium polypeptides in the transmembrane helices 1 and 3. Using oligonucleotides annealing in the regions of the start and stop codons of the gene as primers, a DNA sequence was amplified from nuclear G. sulphuraria DNA by PCR. Compared with the cDNA clone, this sequence contains five additional intervening DNA strings of 50-74bp length. Four of them show typical features of spliceosomal introns with GT-AG borders, and the fifth differs by starting with GC. Three of the supposed introns are located in similar positions as introns of higher plant light-harvesting proteins. Southern blotting and hybridization experiments indicate that G. sulphuraria contains at least three copies of this gene.
高等植物中捕光蛋白基因（lhc基因）已得到充分研究。然而，关于藻类的相应基因却知之甚少，尽管这些知识可能会为光合天线的进化提供有价值的信息。就红藻而言，仅公布了来自单一生物体紫球藻的两个cDNA序列。在此，我们描述了来自另一个物种——嗜热嗜酸红藻硫养加尔迪藻的另一个序列。首次还展示了红藻lhc基因的基因组序列。从硫养加尔迪藻的cDNA文库中，我们分离出一个克隆，该克隆包含一个302个氨基酸的蛋白质开放阅读框，推导分子量为33.86kDa。它与真核生物捕光多肽具有主要结构特征。转运肽和成熟蛋白之间的一个推测切割位点产生了一个119个氨基酸的转运肽和一个183个残基的成熟蛋白。亲水性分析表明，成熟蛋白由三个跨膜螺旋组成。在高等植物中推测与叶绿素a和叶绿素b结合的几个氨基酸残基是保守的。该蛋白在跨膜螺旋1和3中与紫球藻多肽的同一性高达69%，相似性为81%。使用在该基因起始和终止密码子区域退火的寡核苷酸作为引物，通过PCR从硫养加尔迪藻的核DNA中扩增出一个DNA序列。与cDNA克隆相比，该序列包含另外五个长度为50 - 74bp的插入DNA片段。其中四个具有GT - AG边界的剪接体内含子的典型特征，第五个以GC开头不同。三个推测的内含子位于与高等植物捕光蛋白内含子相似的位置。Southern印迹和杂交实验表明，硫养加尔迪藻至少含有该基因的三个拷贝。
