Khatri G S, MacAllister T, Sista P R, Bastia D
Department of Microbiology and Immunology, Duke University Medical Center, Durham, North Carolina 27710.
Cell. 1989 Nov 17;59(4):667-74. doi: 10.1016/0092-8674(89)90012-3.
We have cloned the tus gene that encodes the replication terminator protein of Escherichia coli and have efficiently expressed its gene product. The overproducer strain has been used to purify the terminator (ter) protein in high yield to near homogeneity. The protein is a single 36 kd polypeptide. Using the ter protein and highly purified dnaB helicase, we show that the terminator protein is a DNA sequence-specific contra-helicase, i.e., the protein when bound to its recognition sequence (tau) strongly impedes the ATP-dependent unwinding of double-stranded DNA. This contra-helicase activity is polar, i.e., the impedance to unwinding takes place in only one orientation of the tau sequence. The results illuminate the mechanism of replication termination specifically at tau.
我们已经克隆了编码大肠杆菌复制终止蛋白的tus基因，并高效表达了其基因产物。过量生产菌株已被用于高产纯化终止蛋白（ter），使其接近均一性。该蛋白是一条单一的36 kd多肽。利用ter蛋白和高度纯化的dnaB解旋酶，我们表明终止蛋白是一种DNA序列特异性反解旋酶，即该蛋白与它的识别序列（tau）结合时，会强烈阻碍双链DNA的ATP依赖性解旋。这种反解旋酶活性具有极性，即解旋阻碍仅发生在tau序列的一个方向上。这些结果阐明了复制在tau位点特异性终止的机制。
