Ion-dependent dynamics of DNA ejections for bacteriophage lambda
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Updated: Jun 10, 2026

Following Cell-fate in E. coli After Infection by Phage Lambda
Published on: October 14, 2011
David Wu1, David Van Valen, Qicong Hu
1Division of Engineering and Applied Sciences, California Institute of Technology, Pasadena, California, USA.
Abstract:
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.
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