Dehydrated circular DNA: Circular dichroism of molecules in ethanolic solutions
Dehydrated circular DNA: Circular dichroism of molecules in ethanolic solutions
复制标题
脱水环状 DNA：乙醇溶液中分子的圆二色性
作者：
D. Gray;T. N. Taylor;D. Lang
我们测量了溶液中共价封闭和线性形式的噬菌体PM2 DNA的紫外CD光谱。我们发现，盐或乙醇浓度的增加（高达50%乙醇的重量）降低了两种形式DNA光谱中的长波正CD带，尽管天然共价封闭DNA的光谱总是比线性DNA的光谱具有略大的这些波段。此外，在低Na+浓度下，两种dna在70-80%乙醇中同样能够过渡到a构象。因此，由DNA分子的共价闭合所施加的约束似乎并不妨碍其对这些变化的溶液条件的构象响应。Lang [(1973) J. Mol. Biol. 78, 247-254]通过电子显微镜发现T7 DNA具有凝聚成致密粒子的固有能力，这表明它是多层超线圈。当DNA在0.2M醋酸铵和1 mM EDTA中暴露于乙醇并随后在标本网格上干燥时，共价闭合和线性形式的PM2 DNA也会变得浓缩[Lang， D, Taylor， T. N., Dobyan， D. C. & Gray， D. M. (1976) J. Mol. Biol. 106, 97-107]。在类似条件下，在加入乙醇的0.2M乙酸铵和1 mM EDTA溶液中，我们测量了共价闭合和线性形式DNA的CD光谱。在乙醇浓度下，DNA明显沉淀，两种形式的CD光谱都减少了长波长的正CD带。
We have measured the ultraviolet CD spectra for covalently closed and linear forms of phage PM2 DNA in solution. We find that increased concentrations of salt or ethanol (up to 50% ethanol by weight) depress the long‐wavelength positive CD bands in the spectra of both forms of DNA, although the spectrum of the native covalently closed DNA always has a slightly larger magnitude of these bands than does the spectrum of the linear DNA. In addition, both DNAs are equally capable of undergoing a transition to the A conformation in 70–80% ethanol at low Na+ concentrations. Thus, the constraint imposed by the covalent closure of a DNA molecule does not seem to hinder its conformational response to these changing solution conditions. Lang [(1973) J. Mol. Biol. 78, 247–254] has found by electron microscopy that T7 DNA has an inherent ability to condense into compact particles, suggested to be supercoils of multiple order. Both covalently closed and linear forms of PM2 DNA also become condensed when the DNA, in 0.2M ammonium acetate and 1 mM EDTA, is exposed to ethanol and subsequent drying on specimen grids [Lang, D., Taylor, T. N., Dobyan, D. C. & Gray, D. M. (1976) J. Mol. Biol. 106, 97–107]. Under similar conditions, in solutions of 0.2M ammonium acetate and 1 mM EDTA to which ethanol is added, we have measured the CD spectra of both covalently closed and linear forms of DNA. Below ethanol concentrations at which the DNA obviously precipitates, the CD spectra of both forms have reduced long‐wavelength positive CD bands.