Long Z F, Wang S Y, Nelson N
Department of Biochemistry, Roche Institute of Molecular Biology, Nutley, NJ 07110.
Gene. 1989;76(2):299-312. doi: 10.1016/0378-1119(89)90170-4.
Two clones have been isolated from a genomic library of the moss Physcomitrella patens and a cDNA library of the halotolerant green alga Dunaliella salina. The isolates contain genes coding for the major light-harvesting chlorophyll-a/b-binding protein (CAB) in the photosystem II (PSII) light-harvesting complex (LHCII). The 2544-bp insert of the moss genomic clone contains the complete CAB-coding region and 5' and 3' flanking sequences. The coding region contains an intron of 359 bp which is spanned by a pair of 9-bp perfect direct repeats. There are two CCAAT boxes and five enhancer-like elements related to (G)TGGTTTAAA(G) (Weiher et al., 1983) residing in the intron. Comparisons of the moss cab gene with sequences of light-inducible genes of higher plants reveal homologous and repeated sequences similar to the enhancer element in the 5' region upstream from the TATA and CCAAT boxes thought to be responsive to light inducibility. The 1256-bp algal cDNA contains the complete CAB-coding sequence, a 170-bp 5'-nontranslated region, and a 264-bp 3'-nontranslated region. While the overall homology in the nontranslated regions is low between the cab gene of the moss and that of the alga, the 3'-nontranslated regions of the two contain some sequences that are conserved among the cab genes in higher plants. The deduced amino acid sequences of these two clones are highly conserved except for the N-terminal region. Their hydropathic plots are very similar and both possess three hydrophobic segments that are likely alpha-helical transmembrane segments. The proposed CAB transit peptide sequence of the alga is divergent from that of the moss or higher plants, suggesting that they may have evolved from different origins. Southern blot analysis shows that the cab genes in the moss and the alga, as in higher plants, are encoded by a number of homologous genes constituting a multigene family.
已从苔藓小立碗藓的基因组文库和耐盐绿藻杜氏盐藻的cDNA文库中分离出两个克隆。这些分离物包含编码光系统II（PSII）捕光复合物（LHCII）中主要捕光叶绿素a/b结合蛋白（CAB）的基因。苔藓基因组克隆的2544 bp插入片段包含完整的CAB编码区以及5'和3'侧翼序列。编码区包含一个359 bp的内含子，其由一对9 bp的完美正向重复序列跨越。内含子中存在两个CCAAT盒和五个与(G)TGGTTTAAA(G)相关的增强子样元件（魏尔等人，1983年）。苔藓cab基因与高等植物光诱导基因序列的比较揭示了在TATA盒和CCAAT盒上游5'区域中与增强子元件相似的同源和重复序列，这些序列被认为对光诱导有响应。1256 bp的藻类cDNA包含完整的CAB编码序列、一个170 bp的5'非翻译区和一个264 bp的3'非翻译区。虽然苔藓和藻类的cab基因在非翻译区的总体同源性较低，但两者的3'非翻译区包含一些在高等植物cab基因中保守的序列。除了N端区域外，这两个克隆推导的氨基酸序列高度保守。它们的亲水性图谱非常相似，并且都具有三个可能是α螺旋跨膜片段的疏水片段。藻类拟议的CAB转运肽序列与苔藓或高等植物的不同，表明它们可能起源不同。Southern印迹分析表明，苔藓和藻类中的cab基因与高等植物一样，由构成多基因家族的多个同源基因编码。
