Bramhill D, Kornberg A
Department of Biochemistry, Stanford University School of Medicine, California 94305.
Cell. 1988 Mar 11;52(5):743-55. doi: 10.1016/0092-8674(88)90412-6.
Three tandem repeats of a 13-mer in the AT-rich region are essential to the unique replication origin of E. coli and of remotely related Enterobacteriaceae. These iterated sequences are identified by deletion analysis and sensitivities to endonucleases as the site for initial duplex opening by the initiator dnaA protein. This "open complex" requires ATP and 38 degrees C for optimum formation and stability. The subsequent dnaC-dependent entry of dnaB helicase to form a "prepriming complex" stabilizes the open structure, blocks cleavages by a restriction endonuclease in the 13-mer region, and broadens the endonuclease cutting pattern. We propose that dnaA protein recognizes and successively opens the 13-mer sequences, thereby guiding the entry of dnaB helicase into the duplex preparatory to priming of replication.
富含AT区域中一个13聚体的三个串联重复序列对于大肠杆菌及远缘肠杆菌科细菌独特的复制起点至关重要。通过缺失分析和对核酸内切酶的敏感性鉴定出这些重复序列是起始蛋白dnaA打开双链的位点。这种“开放复合物”形成和稳定的最佳条件是需要ATP和38摄氏度。随后，依赖dnaC的dnaB解旋酶进入形成“预引发复合物”，稳定开放结构，阻止限制性核酸内切酶在13聚体区域的切割，并拓宽核酸内切酶的切割模式。我们提出，dnaA蛋白识别并相继打开13聚体序列，从而引导dnaB解旋酶进入双链，为复制引发做准备。
