Mengeritsky G, Goldenberg D, Mendelson I, Giladi H, Oppenheim A B
Department of Molecular Genetics, Hebrew University-Hadassah Medical School, Jerusalem, Israel.
J Mol Biol. 1993 Jun 5;231(3):646-57. doi: 10.1006/jmbi.1993.1316.
Integration host factor (IHF) is a small, heterodimeric DNA-binding protein of Escherichia coli composed of two subunits, alpha and beta, encoded by the himA and hip genes, respectively. IHF binds to the minor groove at a consensus sequence and bends DNA. We mutagenized the hip gene and studied the activity of the mutant IHF proteins in vivo and in vitro. Substitutions at the C-terminal alpha-helix (alpha-helix 3) reduced IHF activity and relaxed the specificity to DNA without abolishing the ability of IHF to bend DNA. These results indicate that the C-terminal region of Hip participates in determining IHF specificity. Alanine substitutions in beta-strands 2 and 3 generally had no effect on IHF activity in vivo suggesting that individually, many of these residues make only small contributions to the binding of IHF to DNA. Replacing the single amino acid of Hip that differs from HU in a highly conserved region of the arm did not affect IHF activity. This finding led us to conclude that this region of Hip does not contribute to specific DNA recognition by IHF. The binding of IHF to DNA is probably not restricted to one domain, but requires the co-operative participation of a number of regions of the protein.
整合宿主因子（IHF）是大肠杆菌中的一种小型异二聚体DNA结合蛋白，由分别由himA和hip基因编码的α和β两个亚基组成。IHF在共有序列处与小沟结合并使DNA弯曲。我们对hip基因进行诱变，并在体内和体外研究了突变型IHF蛋白的活性。C端α螺旋（α螺旋3）的取代降低了IHF活性，并放宽了对DNA的特异性，而没有消除IHF使DNA弯曲的能力。这些结果表明，Hip的C端区域参与确定IHF的特异性。β链2和3中的丙氨酸取代通常对体内IHF活性没有影响，这表明单独来看，这些残基中的许多对IHF与DNA的结合只起很小的作用。在臂的高度保守区域中替换与HU不同的Hip的单个氨基酸不会影响IHF活性。这一发现使我们得出结论，Hip的这一区域对IHF识别特定DNA没有贡献。IHF与DNA的结合可能不限于一个结构域，而是需要蛋白质多个区域的协同参与。
