Gabig M, Obuchowski M, Srutkowska S, Wegrzyn G
Department of Molecular Biology, University of Gdansk, Poland.
Mol Gen Genet. 1998 Jun;258(5):494-502. doi: 10.1007/s004380050760.
It was previously demonstrated that while lysogenic development of bacteriophage lambda in Escherichia coli proceeds normally at low temperature (20-25 degrees C), lytic development is blocked under these conditions owing to the increased stability of the phage CII protein. This effect was proposed to be responsible for the increased stimulation of the pE promoter, which interferes with expression of the replication genes, leading to inhibition of phage DNA synthesis. Here we demonstrate that the burst size of phage lambda cIb2, which is incapable of lysogenic development, increases gradually over the temperature range from 20 to 37 degrees C, while no phage progeny are observed at 20 degrees C. Contrary to previous reports, it is possible to demonstrate that pE promoter activation by CII may be more efficient at lower temperature. Using density-shift experiments, we found that phage DNA replication is completely blocked at 20 degrees C. Phage growth was also inhibited in cells overexpressing cII, which confirms that CII is responsible for inhibition of phage DNA replication. Unexpectedly, we found that replication of plasmids derived from bacteriophage lambda is neither inhibited at 20 degrees C nor in cells overexpressing cII. We propose a model to explanation the differences in replication observed between lambda phage and lambda plasmid DNA at low temperature.
先前已证明，虽然噬菌体λ在大肠杆菌中的溶原性发育在低温（20 - 25摄氏度）下正常进行，但由于噬菌体CII蛋白稳定性增加，在这些条件下裂解性发育受阻。有人提出这种效应是pE启动子刺激增加的原因，这会干扰复制基因的表达，导致噬菌体DNA合成受到抑制。在此我们证明，无法进行溶原性发育的噬菌体λcIb2的爆发量在20至37摄氏度的温度范围内逐渐增加，而在20摄氏度时未观察到噬菌体后代。与先前的报道相反，可以证明CII对pE启动子的激活在较低温度下可能更有效。通过密度转移实验，我们发现噬菌体DNA复制在20摄氏度时完全受阻。在过表达cII的细胞中噬菌体生长也受到抑制，这证实CII是噬菌体DNA复制受抑制的原因。出乎意料的是，我们发现源自噬菌体λ的质粒复制在20摄氏度时或在过表达cII的细胞中均未受到抑制。我们提出一个模型来解释在低温下观察到的λ噬菌体和λ质粒DNA复制之间的差异。
