Bernard C, Thomas J C, Mazel D, Mousseau A, Castets A M, Tandeau de Marsac N, Dubacq J P
Laboratoire des Biomembranes et Surfaces Cellulaires Végétales (Centre National de la Recherche Scientifique, Unité de Recherches Associée 0311), Ecole Normale Supérieure, Paris, France.
Proc Natl Acad Sci U S A. 1992 Oct 15;89(20):9564-8. doi: 10.1073/pnas.89.20.9564.
The phycobilisome of the eukaryotic unicellular red alga Rhodella violacea presents in some respects an organization that is intermediate between those of the homologous counterparts found in cyanobacteria (the putative chloroplast progenitor) and more advanced, pluricellular red algae. This suggests evolutionary relationships that we investigated at the genome level. The present work describes the sequences of two rhodophytan phycobilisome genes, rpeA and rpeB. These chloroplast genes encode the alpha and beta subunits of phycoerythrin, the major component of the light-harvesting antennae and one of the most abundant cellular proteins in these algae. The amino acid sequences deduced from both rpeA and rpeB present strong homologies with those previously reported for phycoerythrin subunits of cyanobacteria, rhodophyta, and cryptomonads. The main difference with the corresponding cyanobacterial genes was the unexpected occurrence of an intervening sequence that split rpeB into two exons. This intervening sequence presents characteristics of group II introns but lacks several structural domains. Transcriptional analyses showed that the two rpe genes are cotranscribed and that the major RNA species detected corresponds to a mature mRNA lacking the intron. As the phycobiliproteins form a group of closely related polypeptides in cyanobacteria and rhodophyta, the molecular events affecting the corresponding genes, such as the rpeB intron, may be a clue to elucidate some aspects of the molecular processes involved in the evolution of plastid genes.
真核单细胞红藻紫罗藻的藻胆体在某些方面呈现出一种介于蓝细菌（推测的叶绿体祖先）和更高级的多细胞红藻中同源对应物之间的组织形式。这表明了我们在基因组水平上研究的进化关系。目前的工作描述了两个红藻藻胆体基因rpeA和rpeB的序列。这些叶绿体基因编码藻红蛋白的α和β亚基，藻红蛋白是捕光天线的主要成分，也是这些藻类中最丰富的细胞蛋白之一。从rpeA和rpeB推导的氨基酸序列与先前报道的蓝细菌、红藻和隐藻的藻红蛋白亚基的序列具有很强的同源性。与相应蓝细菌基因的主要区别在于意外出现了一个间隔序列，该序列将rpeB分成两个外显子。这个间隔序列具有II类内含子的特征，但缺少几个结构域。转录分析表明，这两个rpe基因是共转录的，检测到的主要RNA种类对应于一个缺少内含子的成熟mRNA。由于藻胆蛋白在蓝细菌和红藻中形成一组密切相关的多肽，影响相应基因的分子事件（如rpeB内含子）可能是阐明质体基因进化过程中分子过程某些方面的线索。
