Real-time observations of single bacteriophage λ DNA ejections in vitro
Real-time observations of single bacteriophage λ DNA ejections in vitro
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DOI：
10.1073/pnas.0703274104
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发表时间：
2007-09-11
影响因子：
11.1
通讯作者：
Phillips, Rob
中科院分区：
文献类型：
--
作者：
Grayson, Paul;Han, Lin;Phillips, Rob
噬菌体基因组释放的物理、化学和结构特征是近年来备受关注的课题。许多理论和实验研究都集中在驱动喷射过程的内力上。王晓明，王晓明，王晓明，等。生物多样性研究进展[J] .中国生物医学工程学报，2005,32(1):457 - 457。]报道了噬菌体T5喷射的荧光显微镜，它在DNA刻痕之间逐步进行，易位速度达到75 kbp/s或更高。目前尚不清楚实际速度有多高。本文报道了噬菌体λ喷射的实时测量，揭示了速度如何取决于关键的物理参数，如基因组长度和缓冲液的离子状态。除了DNA最终释放前的停顿外，整个48.5 kbp的基因组在大约1.5秒内不间断地易位，达到60 kbp/s的速度。该过程对两个参数的影响提供了特别的见解：较短的基因组长度导致较低的速度但较短的总时间，二价镁离子（取代钠）的存在降低了压力，将喷射时间增加到8-11秒。头部内DNA-DNA相互作用产生的压力会影响弹射的开始，但紧密的排列也是摩擦的主要来源：排列更紧密的噬菌体更早开始弹射，但初始速度较低。本研究揭示的抛射细节可能是噬菌体中DNA易位的一般特征，并对其他生物系统中的DNA动力学具有启示意义。
The physical, chemical, and structural features of bacteriophage genome release have been the subject of much recent attention. Many theoretical and experimental studies have centered on the internal forces driving the ejection process. Recently, Mangenot et al. [Mangenot S, Hochrein M, Radler J, Letellier L (2005) Curr Bioi 15:430-435.] reported fluorescence microscopy of phage T5 ejections, which proceeded stepwise between DNA nicks, reaching a translocation speed of 75 kbp/s or higher. It is still unknown how high the speed actually is. This paper reports real-time measurements of ejection from phage lambda, revealing how the speed depends on key physical parameters such as genome length and ionic state of the buffer. Except for a pause before DNA is finally released, the entire 48.5-kbp genome is translocated in approximate to 1.5 s without interruption, reaching a speed of 60 kbp/s. The process gives insights particularly into the effects of two parameters: a shorter genome length results in lower speed but a shorter total time, and the presence of divalent magnesium ions (replacing sodium) reduces the pressure, increasing ejection time to 8-11 s. Pressure caused by DNA-DNA interactions within the head affects the initiation of ejection, but the close packing is also the dominant source of friction: more tightly packed phages initiate ejection earlier, but with a lower initial speed. The details of ejection revealed in this study are probably generic features of DNA translocation in bacteriophages and have implications for the dynamics of DNA in other biological systems.