Laboratory of Molecular Biology, Center for Cancer Research, National Cancer Institute, National Institutes of Health, Bethesda, MD 20892-4264, USA.
Proc Natl Acad Sci U S A. 2011 Sep 6;108(36):14807-12. doi: 10.1073/pnas.1111221108. Epub 2011 Aug 22.
The prophage state of bacteriophage λ is extremely stable and is maintained by a highly regulated level of λ repressor protein, CI, which represses lytic functions. CI regulates its own synthesis in a lysogen by activating and repressing its promoter, P(RM). CI participates in long-range interactions involving two regions of widely separated operator sites by generating a loop in the intervening DNA. We investigated the roles of each individual site under conditions that permitted DNA loop formation by using in vitro transcription assays for the first time on supercoiled DNA that mimics in vivo situation. We confirmed that DNA loops generated by oligomerization of CI bound to its operators influence the autoactivation and autorepression of P(RM) regulation. We additionally report that different configurations of DNA loops are central to this regulation--one configuration further enhances autoactivation and another is essential for autorepression of P(RM).
噬菌体 λ 的前噬菌体状态极其稳定，由高度调控的 λ 阻遏蛋白 CI 维持，CI 抑制裂解功能。CI 通过激活和抑制其启动子 P(RM)来调节溶源菌中的自身合成。CI 通过在 intervening DNA 中产生环，参与涉及两个广泛分离的操纵子区域的远程相互作用。我们首次在模拟体内情况的超螺旋 DNA 上进行体外转录测定，研究了在允许 DNA 环形成的条件下每个单独位点的作用。我们证实，通过与其操纵子结合的 CI 寡聚体生成的 DNA 环影响 P(RM)调节的自动激活和自动抑制。我们还报告说，DNA 环的不同构象是这种调节的核心——一种构象进一步增强了自动激活，另一种构象对于 P(RM)的自动抑制是必不可少的。
