Sarkar Tumpa, Vitoc Iulia, Mukerji Ishita, Hud Nicholas V
School of Chemistry and Biochemistry, Parker H. Petit Institute of Bioengineering and Bioscience, Georgia Institute of Technology, Atlanta, Georgia 30332-0400, USA.
Nucleic Acids Res. 2007;35(3):951-61. doi: 10.1093/nar/gkl1093. Epub 2007 Jan 26.
Controlling the size and shape of DNA condensates is important in vivo and for the improvement of nonviral gene delivery. Here, we demonstrate that the morphology of DNA condensates, formed under a variety of conditions, is shifted completely from toroids to rods if the bacterial protein HU is present during condensation. HU is a non-sequence-specific DNA binding protein that sharply bends DNA, but alone does not condense DNA into densely packed particles. Less than one HU dimer per 225 bp of DNA is sufficient to completely control condensate morphology when DNA is condensed by spermidine. We propose that rods are favored in the presence of HU because rods contain sharply bent DNA, whereas toroids contain only smoothly bent DNA. The results presented illustrate the utility of naturally derived proteins for controlling the shape of DNA condensates formed in vitro. HU is a highly conserved protein in bacteria that is implicated in the compaction and shaping of nucleoid structure. However, the exact role of HU in chromosome compaction is not well understood. Our demonstration that HU governs DNA condensation in vitro also suggests a mechanism by which HU could act as an architectural protein for bacterial chromosome compaction and organization in vivo.
控制DNA凝聚物的大小和形状在体内以及改善非病毒基因递送方面都很重要。在此，我们证明，如果在凝聚过程中存在细菌蛋白HU，那么在各种条件下形成的DNA凝聚物的形态会完全从环形转变为棒状。HU是一种非序列特异性DNA结合蛋白，它能使DNA急剧弯曲，但单独存在时不会将DNA凝聚成紧密堆积的颗粒。当DNA通过亚精胺凝聚时，每225 bp DNA中少于一个HU二聚体就足以完全控制凝聚物的形态。我们提出，在有HU存在的情况下棒状结构更受青睐，因为棒状结构包含急剧弯曲的DNA，而环形结构只包含平滑弯曲的DNA。所呈现的结果说明了天然来源的蛋白质在控制体外形成的DNA凝聚物形状方面的实用性。HU是细菌中一种高度保守的蛋白质，与类核结构的压缩和形成有关。然而，HU在染色体压缩中的确切作用尚未完全了解。我们证明HU在体外控制DNA凝聚，这也提示了一种机制，通过该机制HU可以在体内作为细菌染色体压缩和组织的结构蛋白发挥作用。
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