Bartok K, Denhardt D T
J Biol Chem. 1976 Jan 25;251(2):530-5.
Experiments with the Neurospora crassa single strand-specific endonuclease have provided evidence for the existence of regions of partially single-stranded character in covalently closed superhelical replicative form DNA of phiX174. The nuclease converts the superhelical molecules to either singly hit relaxed circular or doubly hit linear molecules. We show that the initial cleavage of phiX174 superhelical DNA is a "nick" bounded by a 5'-phosphate and a 3'-hydroxyl; no nucleotides are excised as evidenced by the ability of T4-polynucleotide ligase to reform the phosphodiester bond. The nick can be found in either strand of the double-stranded DNA and is either randomly distributed or at least can be found at any one of many possible locations in the genome. Thus, the regions in phiX174 superhelical molecules that are sensitive to the N. crassa nuclease do not occur at highly specific sites in the genome.
对粗糙脉孢菌单链特异性核酸内切酶的实验已为在φX174的共价闭合超螺旋复制型DNA中存在部分单链特征区域提供了证据。该核酸内切酶将超螺旋分子转化为单切口松弛环状分子或双切口线性分子。我们表明，φX174超螺旋DNA的初始切割是一个由5'-磷酸和3'-羟基界定的“切口”；T4-多核苷酸连接酶能够重新形成磷酸二酯键，这证明没有核苷酸被切除。该切口可在双链DNA的任何一条链中找到，并且要么是随机分布的，要么至少可以在基因组中许多可能位置的任何一处找到。因此，φX174超螺旋分子中对粗糙脉孢菌核酸内切酶敏感的区域并非出现在基因组中的高度特异性位点。
