INFLUENCES OF MACROMOLECULAR CROWDING ON BIOCHEMICAL SYSTEMS

细菌染色体的DNA定位于一个紧凑的身体中，称为 类核生物。细菌类核素已被广泛研究，但 类核稳定的基础仍然难以捉摸。 大肠杆菌的细胞质非常集中在大分子中，给 有可能产生大分子拥挤效应。现在 结果表明，拥挤增强DNA-DNA之间的相互作用 结合蛋白和细胞DNA可能提供重要的 细菌类核糖核酸致密形式的稳定力。 指数期和稳定期细胞DNA结合蛋白组分 用亲和层析法分离纯化了大肠杆菌提取物。 DNA-纤维素。这些组分将DNA转化为 在没有或存在添加的情况下，比较易沉淀的形式 聚合物。在没有聚合物的情况下，大量的蛋白质 必填项。在聚乙二醇或聚乙烯吡咯烷酮存在的情况下， 所需的DNA结合蛋白数量要少得多， 表明这些聚合物具有大分子拥挤效应。这个 在拥挤的条件下加强约束似乎解决了一个悖论 DNA结合蛋白的细胞丰度和 在早期的体外研究中所需的剂量。 DNA结合蛋白组份中的“组蛋白样”蛋白Hu 在存在的情况下优先结合到片状DNA中 聚合物。以大致相同的量提纯HU会导致类似的 将DNA转化为易沉淀(“浓缩”)的形式。拥挤- 促进蛋白质与DNA结合促进DNA缩合 DNA为系统的稳定提供了一个模型，例如 细菌类核体或动质体DNA。

The DNA of a bacterial chromosome is localized in a compact body called the nucleoid. Bacterial nucleoids have been extensively studied, but the basis of nucleoid stabilization has remained elusive. The cytoplasm of E. coli is very concentrated in macromolecules, giving a potential for large macromolecular crowding effects. The present results suggest that crowding-enhancement of the interaction between DNA- binding proteins and the cellular DNA may provide an important stabilizing force for the compact form of DNA in the bacterial nucleoid. DNA-binding protein fractions from exponential and stationary phase cell extracts of E. coli were isolated by affinity chromatography on native DNA-cellulose. The ability of these fractions to convert DNA into a readily-sedimented form was compared in the absence or presence of added polymers. In the absence of polymers, large amounts of the proteins were required. In the presence of polyethylene glycol or polyvinylpyrrolidone, much smaller amounts of the DNA-binding proteins were required, indicating a macromolecular crowding effect from these polymers. The enhanced binding under crowded conditions appears to resolve a paradox between the cellular abundance of the DNA-binding proteins and the amounts required in earlier in vitro studies. The "histone-like" protein HU from the DNA-binding protein fraction was preferentially incorporated into the pelleted DNA in the presence of polymers. Purified HU at roughly similar amounts caused a similar conversion of DNA to a readily-sedimentable ("condensed") form. Crowding- enhancement of DNA condensation by promoting the binding of proteins to the DNA provides a model for the stabilization of systems such as the bacterial nucleoid or kinetoplast DNA.