Division of Engineering and Applied Sciences, California Institute of Technology, Pasadena, California, USA.
Biophys J. 2010 Aug 9;99(4):1101-9. doi: 10.1016/j.bpj.2010.06.024.
We studied the control parameters that govern the dynamics of in vitro DNA ejection in bacteriophage lambda. Previous work demonstrated that bacteriophage DNA is highly pressurized, and this pressure has been hypothesized to help drive DNA ejection. Ions influence this process by screening charges on DNA; however, a systematic variation of salt concentrations to explore these effects has not been undertaken. To study the nature of the forces driving DNA ejection, we performed in vitro measurements of DNA ejection in bulk and at the single-phage level. We present measurements on the dynamics of ejection and on the self-repulsion force driving ejection. We examine the role of ion concentration and identity in both measurements, and show that the charge of counterions is an important control parameter. These measurements show that the mobility of ejecting DNA is independent of ionic concentrations for a given amount of DNA in the capsid. We also present evidence that phage DNA forms loops during ejection, and confirm that this effect occurs using optical tweezers.
我们研究了控制噬菌体 λ 中体外 DNA 喷射动力学的控制参数。先前的工作表明，噬菌体 DNA 受到很高的压力，并且有人假设这种压力有助于推动 DNA 喷射。离子通过在 DNA 上屏蔽电荷来影响这个过程；然而，尚未进行系统地改变盐浓度来探索这些影响。为了研究驱动 DNA 喷射的力的性质，我们在体外进行了批量和单噬菌体水平的 DNA 喷射测量。我们展示了有关喷射动力学和驱动喷射的自排斥力的测量结果。我们研究了离子浓度和身份在这两个测量中的作用，并表明抗衡离子的电荷是一个重要的控制参数。这些测量表明，对于衣壳中给定量的 DNA，喷射 DNA 的迁移率与离子浓度无关。我们还提供了噬菌体 DNA 在喷射过程中形成环的证据，并使用光学镊子证实了这一效应。
