Department of Physics, Emory University, 400 Dowman Drive, Atlanta, GA 30322, USA.
Nucleic Acids Res. 2013 Jun;41(11):5746-56. doi: 10.1093/nar/gkt298. Epub 2013 Apr 24.
The lytic-lysogenic decision in bacteriophage 186 is governed by the 186 CI repressor protein in a unique way. The 186 CI is proposed to form a wheel-like oligomer that can mediate either wrapped or looped nucleoprotein complexes to provide the cooperative and competitive interactions needed for regulation. Although consistent with structural, biochemical and gene expression data, many aspects of this model are based on inference. Here, we use atomic force microscopy (AFM) to reveal the various predicted wrapped and looped species, and new ones, for CI regulation of lytic and lysogenic transcription. Automated AFM analysis showed CI particles of the predicted dimensions on the DNA, with CI multimerization favoured by DNA binding. Measurement of the length of the wrapped DNA segments indicated that CI may move on the DNA, wrapping or releasing DNA on either side of the wheel. Tethered particle motion experiments were consistent with wrapping and looping of DNA by CI in solution, where in contrast to λ repressor, the looped species were exceptionally stable. The CI regulatory system provides an intriguing comparison with that of nucleosomes, which share the ability to wrap and release similar sized segments of DNA.
噬菌体 186 的裂解-溶源决定是由 186 CI 阻遏蛋白以一种独特的方式控制的。186 CI 被提议形成一种轮状寡聚体，它可以介导包裹或环状核蛋白复合物，为调节提供所需的协同和竞争相互作用。尽管该模型与结构、生化和基因表达数据一致，但许多方面都是基于推断。在这里，我们使用原子力显微镜（AFM）来揭示 CI 调节裂解和溶源转录的各种预测的包裹和环状物种，以及新的物种。自动 AFM 分析显示，CI 粒子在 DNA 上具有预测的尺寸，DNA 结合有利于 CI 多聚化。包裹 DNA 片段的长度测量表明，CI 可能在 DNA 上移动，在轮子的两侧包裹或释放 DNA。系绳粒子运动实验与 CI 在溶液中对 DNA 的缠绕和环化一致，与 λ 阻遏物相比，环状物种异常稳定。CI 调节系统与核小体的调节系统形成了有趣的对比，核小体具有包裹和释放类似大小的 DNA 片段的能力。
