Conley P B, Lemaux P G, Grossman A
Department of Plant Biology, Carnegie Institution of Washington, Stanford, CA 94305.
J Mol Biol. 1988 Feb 5;199(3):447-65. doi: 10.1016/0022-2836(88)90617-1.
The major light-harvesting complex in eukaryotic red algae and prokaryotic cyanobacteria is the phycobilisome, a water-soluble complex located on the outer surface of the photosynthetic membranes and composed of both pigmented phycobiliproteins (85%) and non-pigmented linker (15%) polypeptides. The phycobiliproteins are encoded by a gene family and exhibit varying degrees of sequence homology (25 to 55%). Some cyanobacteria can maximize the absorption of prevalent wavelengths of light by adjusting the phycobiliprotein composition of the phycobilisome, a process called complementary chromatic adaptation. In the chromatically adapting species Fremyella displosiphon, there are at least two sets of phycocyanin genes; one is transcribed as two red light-induced transcripts and the other is encoded on a single transcript present in both red and green light. We have determined the complete nucleotide sequences of both sets of phycocyanin subunit genes and their associated 5' and 3' regulatory regions. Based on S1 nuclease protection experiments, the transcripts (1600 and 3800 bases) encoding the inducible phycocyanin subunits have the same 5' end, and possible mechanisms for their synthesis are presented. The 5' end of the 1500-base transcript encoding the constitutive phycocyanin subunits was determined and revealed an Escherichia coli-like "-10" and "-35" region, and sequences near the transcription initiation site homologous to the analogous region of the phycocyanin gene set of Anabaena sp. 7120. Determination of the 3' ends of the transcripts encoding both F. diplosiphon phycocyanin gene sets revealed regions of potential secondary structure that may be important for transcription termination and/or transcript stability. In addition, the sequence of an open reading frame (encoding a 30 kDa polypeptide), located 3' to the constitutive phycocyanin gene set in F. diplosiphon and highly conserved in at least three cyanobacterial species, is presented. The same high degree of sequence homology between the two F. diplosiphon PC alpha and PC beta sequences (85 and 77%, respectively) was found at both the nucleotide and amino acid levels, and similar results were obtained for interspecies comparisons. Implications of these homologies with regard to the evolution of phycobiliprotein subunits are discussed.
真核红藻和原核蓝细菌中的主要捕光复合体是藻胆体，它是一种位于光合膜外表面的水溶性复合体，由色素藻胆蛋白（85%）和非色素连接子（15%）多肽组成。藻胆蛋白由一个基因家族编码，表现出不同程度的序列同源性（25%至55%）。一些蓝细菌可以通过调整藻胆体的藻胆蛋白组成来最大化对常见波长光的吸收，这一过程称为互补色适应。在进行色适应的物种费氏藻中，至少有两组藻蓝蛋白基因；一组转录为两个红光诱导转录本，另一组编码在红光和绿光中都存在的单个转录本上。我们已经确定了这两组藻蓝蛋白亚基基因及其相关的5'和3'调控区的完整核苷酸序列。基于S1核酸酶保护实验，编码可诱导藻蓝蛋白亚基的转录本（1600和3800个碱基）具有相同的5'末端，并提出了它们的合成可能机制。确定了编码组成型藻蓝蛋白亚基的1500个碱基转录本的5'末端，发现了一个类似大肠杆菌的“-10”和“-35”区域，以及转录起始位点附近与鱼腥藻7120藻蓝蛋白基因集类似区域同源的序列。确定费氏藻两组藻蓝蛋白基因转录本的3'末端，揭示了可能对转录终止和/或转录本稳定性很重要的潜在二级结构区域。此外，还给出了位于费氏藻组成型藻蓝蛋白基因集下游且在至少三种蓝细菌物种中高度保守的一个开放阅读框（编码一个30 kDa多肽）的序列。在核苷酸和氨基酸水平上，费氏藻的两个藻蓝蛋白α和藻蓝蛋白β序列之间都发现了相同程度的高度序列同源性（分别为85%和77%），种间比较也得到了类似结果。讨论了这些同源性对藻胆蛋白亚基进化的影响。
