渗透压：阻止或促进DNA从噬菌体排出
Osmotic pressure: resisting or promoting DNA ejection from phage
摘要：
最近的体外实验表明，当排出的DNA在排出过程中被DNA酶I消化时，周围的渗透压可以部分地阻止噬菌体的DNA排出。我们认为，在这项工作中结合实验技术（渗透抑制没有DNaseI监测的UV吸光度，脉冲场电泳，和cryo-EM可视化）和简单的缩放模型，完整的基因组（即未消化）在拥挤的环境中喷射，相反，增强或最终完成的帮助下，从DNA凝聚引起的渗透应力本身的拉力。这表明，在体内，细胞质的应激将促进噬菌体DNA排出，而不是抵制它。进一步添加的DNA结合蛋白在拥挤的条件下，显示出提高排出的程度。我们还发现了一些最佳拥挤条件，在这些条件下，排出后留在衣壳中的DNA含量最大，这与近20年前观察到的最大DNA包装效率进入病毒衣壳的最佳条件密切相关。这一发现的生物后果进行了讨论。
英文摘要：
Recent in vitro experiments have shown that DNA ejection from bacteriophage can be partially stopped by surrounding osmotic pressure when ejected DNA is digested by DNase I on the course of ejection. We argue in this work by combination of experimental techniques (osmotic suppression without DNaseI monitored by UV absorbance, pulse-field electrophoresis, and cryo-EM visualization) and simple scaling modeling that intact genome (i.e. undigested) ejection in a crowded environment is, on the contrary, enhanced or eventually complete with the help of a pulling force resulting from DNA condensation induced by the osmotic stress itself. This demonstrates that in vivo, the osmotically stressed cell cytoplasm will promote phage DNA ejection rather than resisting it. The further addition of DNA-binding proteins under crowding conditions is shown to enhance the extent of ejection. We also found some optimal crowding conditions for which DNA content remaining in the capsid upon ejection is maximum, which correlates well with the optimal conditions of maximum DNA packaging efficiency into viral capsids observed almost 20 years ago. Biological consequences of this finding are discussed.
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