Maeda Y, Ohtsubo E
Institute of Applied Microbiology, University of Tokyo, Japan.
J Mol Biol. 1987 Apr 20;194(4):691-8. doi: 10.1016/0022-2836(87)90246-4.
Differential scanning calorimetry (DSC) was carried out to analyze the transition of helix to coil state of DNA, using ColE1 DNA molecules digested with EcoRI. The DSC curves showed multimodal transition, consisting of nine to 11 peaks over a temperature range, depending on the ionic strength of the DNA solution. These DSC curves were essentially in good agreement with the optical melting curves of ColE1 DNA. The theoretical melting profiles of ColE1 DNA were predicted from calculations based on the helix-coil transition theory and the nucleotide sequence of the DNA. These profiles resembled the DSC curves and made it possible to assign the peaks seen in the DSC curves to the helix-coil transition of particular regions of the nucleotide sequence of ColE1. The helix-coil transition of each of the small genes gave rise to a single peak in the DSC curve, while the helix-coil transition of large genes contributed to two or more peaks in the DSC curve. This multimodal transition within a single coding region might correspond to the melting of individual segments encoding the different domains of the proteins. The helix-coil transition at the specific sites including ori, the origin of replication of ColE1, was also found to occur in a particular temperature range. DSC, a simple method, is thus useful for analyzing the multimodal helix-coil transition of DNA, and for providing information on the genetic organization of DNA.
采用差示扫描量热法（DSC）对经EcoRI酶切的ColE1 DNA分子进行分析，以研究DNA从螺旋状态到卷曲状态的转变。DSC曲线显示出多峰转变，在一定温度范围内有9至11个峰，这取决于DNA溶液的离子强度。这些DSC曲线与ColE1 DNA的光学熔解曲线基本一致。基于螺旋-卷曲转变理论和DNA的核苷酸序列计算预测了ColE1 DNA的理论熔解曲线。这些曲线与DSC曲线相似，使得能够将DSC曲线中观察到的峰与ColE1核苷酸序列特定区域的螺旋-卷曲转变对应起来。每个小基因的螺旋-卷曲转变在DSC曲线中产生一个单峰，而大基因的螺旋-卷曲转变在DSC曲线中产生两个或更多峰。单个编码区域内的这种多峰转变可能对应于编码蛋白质不同结构域的各个片段的熔解。还发现在包括ori（ColE1的复制起点）在内的特定位点的螺旋-卷曲转变发生在特定温度范围内。因此，DSC作为一种简单的方法，对于分析DNA的多峰螺旋-卷曲转变以及提供有关DNA遗传组织的信息很有用。
