Greenstein D, Zinder N D, Horiuchi K
Rockefeller University, New York, NY 10021.
Proc Natl Acad Sci U S A. 1988 Sep;85(17):6262-6. doi: 10.1073/pnas.85.17.6262.
We present data which show that the Escherichia coli integration host factor (IHF) is an activator of phage f1 DNA replication. Phage f1 poorly infects bacterial strains lacking IHF because IHF is required for efficient expression of F-pili, the receptor for f1 phage. However, when F- strains are transfected with f1 DNA the phage replicates in IHF mutants (himA, himD, or himA himD) at a rate of only 3% of that in wild-type bacteria. A plasmid dependent on the f1 replicon fails to transform IHF mutants. By gel retardation analysis, we show that IHF specifically binds to the origin of replication. DNase I "footprinting" experiments demonstrate that IHF binds to multiple sites within the replication enhancer sequence, a cis-acting, A + T-rich sequence that potentiates f1 DNA replication. Moreover, the effect of IHF mutation on f1 growth is suppressed by initiator protein (f1 gene II) mutations that restore efficient replication from origins that lack a functional replication enhancer sequence. This genetic evidence supports the conclusion that the replication enhancer sequence is the site of action of IHF.
我们提供的数据表明，大肠杆菌整合宿主因子（IHF）是噬菌体f1 DNA复制的激活因子。噬菌体f1很难感染缺乏IHF的细菌菌株，因为f1噬菌体的受体F菌毛的有效表达需要IHF。然而，当用f1 DNA转染F-菌株时，噬菌体在IHF突变体（himA、himD或himA himD）中复制的速率仅为野生型细菌中的3%。依赖于f1复制子的质粒无法转化IHF突变体。通过凝胶阻滞分析，我们表明IHF特异性结合到复制起点。DNA酶I“足迹”实验证明，IHF结合到复制增强子序列内的多个位点，该序列是一个顺式作用的富含A+T的序列，可增强f1 DNA复制。此外，起始蛋白（f1基因II）突变可抑制IHF突变对f1生长的影响，这些突变可从缺乏功能性复制增强子序列的起点恢复有效复制。这一遗传学证据支持了复制增强子序列是IHF作用位点的结论。
