Bergsland K J, Haselkorn R
Department of Molecular Genetics and Cell Biology, University of Chicago, Illinois 60637.
J Bacteriol. 1991 Jun;173(11):3446-55. doi: 10.1128/jb.173.11.3446-3455.1991.
RNA polymerases of cyanobacteria contain a novel core subunit, gamma, which is absent from the RNA polymerases of other eubacteria. The genes encoding the three largest subunits of RNA polymerase, including gamma, have been isolated from the cyanobacterium Anabaena sp. strain PCC 7120. The genes are linked in the order rpoB, rpoC1, rpoC2 and encode the beta, gamma, and beta' subunits, respectively. These genes are analogous to the rpoBC operon of Escherichia coli, but the functions of rpoC have been split in Anabaena between two genes, rpoC1 and rpoC2. The DNA sequence of the rpoC1 gene was determined and shows that the gamma subunit corresponds to the amino-terminal half of the E. coli beta' subunit. The gamma protein contains several conserved domains found in the largest subunits of all bacterial and eukaryotic RNA polymerases, including a potential zinc finger motif. The spliced rpoC1 gene from spinach chloroplast DNA was expressed in E. coli and shown to encode a protein immunologically related to Anabaena gamma. The similarities in the RNA polymerase gene products and gene organizations between cyanobacteria and chloroplasts support the cyanobacterial origin of chloroplasts and a divergent evolutionary pathway among eubacteria.
蓝细菌的RNA聚合酶含有一种新的核心亚基γ，而其他真细菌的RNA聚合酶中没有这种亚基。编码RNA聚合酶三个最大亚基（包括γ）的基因已从蓝细菌鱼腥藻PCC 7120中分离出来。这些基因按rpoB、rpoC1、rpoC2的顺序相连，分别编码β、γ和β'亚基。这些基因类似于大肠杆菌的rpoBC操纵子，但在鱼腥藻中，rpoC的功能被分成了两个基因rpoC1和rpoC2。测定了rpoC1基因的DNA序列，结果表明γ亚基对应于大肠杆菌β'亚基的氨基末端一半。γ蛋白含有在所有细菌和真核生物RNA聚合酶最大亚基中发现的几个保守结构域，包括一个潜在的锌指基序。来自菠菜叶绿体DNA的剪接rpoC1基因在大肠杆菌中表达，并显示编码一种与鱼腥藻γ蛋白有免疫相关性的蛋白。蓝细菌和叶绿体之间RNA聚合酶基因产物和基因组织的相似性支持了叶绿体的蓝细菌起源以及真细菌之间不同的进化途径。
