Protein-mediated DNA looping is fundamental to gene regulation and such loops occur stochastically in purified systems. Additional proteins increase the probability of looping, but these probabilities maintain a broad distribution. For example, the probability of lac repressor-mediated looping in individual molecules ranged 0-100%, and individual molecules exhibited representative behavior only in observations lasting an hour or more. Titrating with HU protein progressively compacted the DNA without narrowing the 0-100% distribution. Increased negative supercoiling produced an ensemble of molecules in which all individual molecules more closely resembled the average. Furthermore, in only twelve minutes of observation, well within the doubling time of the bacterium, most molecules exhibited the looping probability of the ensemble. DNA supercoiling, an inherent feature of all genomes, appears to impose time-constrained, emergent behavior on otherwise random molecular activity.

中文翻译：

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负DNA超螺旋使蛋白质介导的环在细菌加倍时间内具有确定性和遍历性

蛋白质介导的DNA循环是基因调控的基础，这种循环在纯化系统中随机发生。其他蛋白质会增加出现环的可能性，但是这些概率保持广泛的分布。例如，单个分子中lac阻遏物介导的环化的可能性范围为0-100％，并且单个分子仅在持续一小时或更长时间的观察中才表现出代表性行为。用HU蛋白滴定可逐渐压实DNA，而不会缩小0-100％的分布。负超螺旋的增加会产生一个分子集合，其中所有单个分子都更接近平均值。此外，在仅仅十二分钟的观察中，恰好在细菌的倍增时间内，大多数分子表现出合奏的循环概率。DNA超螺旋