Cozens A L, Walker J E
J Mol Biol. 1987 Apr 5;194(3):359-83. doi: 10.1016/0022-2836(87)90667-x.
The nucleotide sequence has been determined of two regions of DNA cloned from the cyanobacterium Synechococcus 6301. The larger, 8890 base-pairs in length, contains a cluster of seven genes for subunits of ATP synthase. The order of the genes is a:c:b':b:delta:alpha:gamma, b' being a duplicated and diverged form of b. As in the Escherichia coli unc operon, the a gene is preceded by a gene for a small hydrophobic and basic protein. The hydrophobic profile of the potential gene product suggests that its secondary structure is similar to the uncI protein. The smaller DNA fragment, 4737 base-pairs in length, is separated from the larger by at least 15 X 10(3) base-pairs of DNA. It contains a cluster of two genes encoding ATP synthase subunits beta and epsilon. Both clusters of ATP synthase genes are preceded by sequences resembling the -10 (Pribnow) box of E. coli promoters and are followed by sequences able to form stable stem-loop structures that might serve to terminate transcription. These features and the small intergenic non-coding sequences suggest that the clusters are operons, for which the names atp1 and atp2 are proposed. The order of genes within the two clusters is very similar to the gene order in the E. coli unc operon. However, it is most closely related to the arrangement of genes for ATP synthetase subunits a:c:b:alpha and beta:epsilon in two clusters in pea chloroplast DNA. This close relationship between chloroplasts and the cyanobacterium is also evident from comparisons of the sequences of ATP synthase subunits; the Synechococcus proteins are much more closely related to chloroplast homologues than to those in other bacteria or in mitochondria. It is further supported by the cyanobacterial b and b' proteins which, in common with their chloroplast counterpart, subunit I, have extra amino-terminal extensions relative to the E. coli b protein. This extension is known to be removed by post-translational processing in the chloroplast, but its function is obscure. It also seems likely that the cyanobacterial and chloroplast ATP synthases have important similarities in subunit composition. For example, the presence of two related genes, b and b', in the cyanobacterium suggests that its ATP synthase is a complex of nine polypeptides, and that it may have single copies of related b and b' proteins rather than two copies of identical b subunits as found in the E. coli enzyme.4+off
已确定从蓝藻聚球藻6301克隆的两个DNA区域的核苷酸序列。较大的区域长度为8890个碱基对，包含一组七个ATP合酶亚基的基因。基因顺序为a:c:b':b:δ:α:γ，其中b'是b的重复且有差异的形式。与大肠杆菌unc操纵子一样，a基因之前是一个小的疏水碱性蛋白的基因。潜在基因产物的疏水图谱表明其二级结构与uncI蛋白相似。较小的DNA片段长度为4737个碱基对，与较大片段被至少15×10³个碱基对的DNA隔开。它包含一组两个编码ATP合酶亚基β和ε的基因。两组ATP合酶基因之前都有类似于大肠杆菌启动子的-10（普里布诺）框的序列，之后是能够形成稳定茎环结构的序列，这些结构可能用于终止转录。这些特征以及小的基因间非编码序列表明这些簇是操纵子，为此提出了atp1和atp2的名称。两个簇内的基因顺序与大肠杆菌unc操纵子中的基因顺序非常相似。然而，它与豌豆叶绿体DNA中两个簇中ATP合酶亚基a:c:b:α和β:ε的基因排列最为密切相关。从ATP合酶亚基序列的比较中也可以明显看出叶绿体与蓝藻之间的这种密切关系；聚球藻蛋白与叶绿体同源物的关系比与其他细菌或线粒体中的同源物更为密切。蓝藻的b和b'蛋白与它们的叶绿体对应物亚基I一样，相对于大肠杆菌b蛋白有额外的氨基末端延伸，这进一步支持了这一点。已知这种延伸在叶绿体中通过翻译后加工被去除，但其功能尚不清楚。蓝藻和叶绿体ATP合酶在亚基组成上似乎也可能有重要的相似之处。例如，蓝藻中存在两个相关基因b和b'，这表明其ATP合酶是一种由九个多肽组成的复合物，并且它可能有相关b和b'蛋白的单拷贝，而不是像大肠杆菌酶中那样有两个相同b亚基的拷贝。
