Puhl H L, Behe M J
Department of Chemistry, Lehigh University, Bethlehem, PA 18015.
J Mol Biol. 1995 Feb 3;245(5):559-67. doi: 10.1006/jmbi.1994.0046.
The synthetic polymer poly(dA).poly(dT) was long thought to be refractory to nucleosome formation. Several years ago our laboratory demonstrated that the polymer could be mixed with authentic nucleosomes in a low-salt exchange procedure to form a nucleoprotein complex that behaved in a manner identical with that of nucleosomes. Competitive exchange assays at 37 degrees C showed that the homopolymer reconstituted about as well as heterogenous-sequence DNA. However, studies by other laboratories have shown that the conformation of poly(dA).poly(dT) depends on temperature; the polymer converts from its well-known, atypical structure, found at ambient temperature, to a conformation more closely resembling a canonical B form as temperature is increased. We have measured the ability of the homopurine.homopyrimidine to form nucleosomes as a function of temperature. It is seen that poly(dA).poly(dT) forms nucleosomes more strongly as the temperature of the exchange mixture is increased, so that poly(dA).(dT) outcompetes heterogeneous-sequence DNA for histones at elevated temperatures.
合成聚合物聚（dA）·聚（dT）长期以来被认为难以形成核小体。几年前，我们实验室证明，在低盐交换过程中，该聚合物可与真实的核小体混合，形成一种核蛋白复合物，其行为方式与核小体相同。37℃下的竞争性交换试验表明，这种同聚物的重构效果与异源序列DNA相当。然而，其他实验室的研究表明，聚（dA）·聚（dT）的构象取决于温度；随着温度升高，该聚合物从其在环境温度下常见的非典型结构转变为更接近标准B型的构象。我们已测量了这种同嘌呤·同嘧啶聚合物形成核小体的能力随温度的变化情况。可以看到，随着交换混合物温度升高，聚（dA）·聚（dT）形成核小体的能力增强，以至于在高温下，聚（dA）·聚（dT）比异源序列DNA更能竞争组蛋白。
