Troxler R F, Lin S, Offner G D
Department of Biochemistry, Boston University School of Medicine, Massachusetts 02118.
J Biol Chem. 1989 Dec 5;264(34):20596-601.
Allophycocyanin and phycocyanin in the red alga (Cyanidium caldarium) are chloroplast-encoded, light-harvesting accessory pigments composed of alpha and beta subunit polypeptides (17-19 kDa) to which 1 or more residues of the heme-derived bile pigment chromophore phycocyanobilin are attached by cysteinyl thioether linkages (Offner, G.D., and Troxler, R.F. (1983) J. Biol. Chem. 258, 9931-9940). Western blot experiments utilizing phycobiliprotein antisera revealed that immunoreactive allophycocyanin and phycocyanin apoproteins were absent in cells grown in the dark and present in cells exposed to light. Northern blot experiments using genomic DNA hybridization probes indicated that phycobiliprotein mRNAs were absent in the dark, whereas cells exposed to light contained two allophycocyanin mRNA transcripts, 1.4 and 1.6 kilobases in length, and one phycocyanin mRNA transcript, 3.0 kilobases in length, providing evidence that phycobiliproteins are encoded in photogenes which are only transcriptionally active in the light. Northern and Western analyses demonstrated that cells incubated in the dark with the heme precursor delta-aminolevulinate contained allophycocyanin and phycocyanin mRNAs and apoproteins, indistinguishable in size, number, and quantity from those made in the light. Cells incubated in the dark with delta-aminolevulinate, protoporphyrin IX, or heme, but not biliverdin or phycocyanobilin, synthesized allophycocyanin and phycocyanin alpha and beta apoproteins, suggesting a role for heme in the control phycobiliprotein gene expression. Cells incubated with heme in the dark produced allophycocyanin and phycocyanin mRNA transcripts, but did not produce mRNAs for four other photogenes coding for a P-700 reaction center protein, a 32-kDa herbicide-binding protein, and the large and small subunits of ribulose-bisphosphate carboxylase. These results show, for the first time, that heme is a regulatory factor specifically involved in transcriptional regulation of chloroplast genes for phycobiliproteins.
红藻（嗜热栖热放线菌）中的别藻蓝蛋白和藻蓝蛋白是叶绿体编码的捕光辅助色素，由α和β亚基多肽（17 - 19 kDa）组成，1个或更多个源自血红素的胆汁色素发色团藻蓝胆素残基通过半胱氨酰硫醚键与之相连（奥夫纳，G.D.，和特罗克斯勒，R.F.（1983年）《生物化学杂志》258卷，9931 - 9940页）。利用藻胆蛋白抗血清进行的蛋白质免疫印迹实验表明，在黑暗中生长的细胞中不存在免疫反应性别藻蓝蛋白和藻蓝蛋白脱辅基蛋白，而在光照下的细胞中存在。使用基因组DNA杂交探针进行的RNA印迹实验表明，黑暗中藻胆蛋白mRNA不存在，而光照下的细胞含有两种长度分别为1.4和1.6千碱基的别藻蓝蛋白mRNA转录本，以及一种长度为3.0千碱基的藻蓝蛋白mRNA转录本，这证明藻胆蛋白是由仅在光照下转录活跃的光合基因编码的。RNA印迹和蛋白质免疫印迹分析表明，在黑暗中用血红素前体δ-氨基乙酰丙酸孵育的细胞含有别藻蓝蛋白和藻蓝蛋白mRNA及脱辅基蛋白，其大小、数量和含量与光照下产生的无法区分。在黑暗中用δ-氨基乙酰丙酸、原卟啉IX或血红素孵育的细胞，但不是用胆绿素或藻蓝胆素孵育的细胞，合成了别藻蓝蛋白和藻蓝蛋白α和β脱辅基蛋白，这表明血红素在控制藻胆蛋白基因表达中起作用。在黑暗中用血红素孵育的细胞产生了别藻蓝蛋白和藻蓝蛋白mRNA转录本，但没有产生另外四个光合基因的mRNA，这四个光合基因分别编码一种P - 700反应中心蛋白、一种32 kDa除草剂结合蛋白以及核酮糖-1,5-二磷酸羧化酶的大亚基和小亚基。这些结果首次表明，血红素是一种特异性参与叶绿体藻胆蛋白基因转录调控的调节因子。
