Calb R, Davidovitch A, Koby S, Giladi H, Goldenberg D, Margalit H, Holtel A, Timmis K, Sanchez-Romero J M, de Lorenzo V, Oppenheim A B
Department of Molecular Genetics and Biotechnology, Hadassah Medical School, The Hebrew University, Jerusalem, Israel.
J Bacteriol. 1996 Nov;178(21):6319-26. doi: 10.1128/jb.178.21.6319-6326.1996.
Integration host factor (IHF) is a DNA-binding and -bending protein that has been found in a number of gram-negative bacteria. Here we describe the cloning, sequencing, and functional analysis of the genes coding for the two subunits of IHF from Pseudomonas putida. Both the ihfA and ihfB genes of P. putida code for 100-amino-acid-residue polypeptides that are 1 and 6 residues longer than the Escherichia coli IHF subunits, respectively. The P. putida ihfA and ihfB genes can effectively complement E. coli ihf mutants, suggesting that the P. putida IHF subunits can form functional heterodimers with the IHF subunits of E. coli. Analysis of the amino acid differences between the E. coli and P. putida protein sequences suggests that in the evolution of IHF, amino acid changes were mainly restricted to the N-terminal domains and to the extreme C termini. These changes do not interfere with dimer formation or with DNA recognition. We constructed a P. putida mutant strain carrying an ihfA gene knockout and demonstrated that IHF is essential for the expression of the P(U) promoter of the xyl operon of the upper pathway of toluene degradation. It was further shown that the ihfA P. putida mutant strain carrying the TOL plasmid was defective in the degradation of the aromatic model compound benzyl alcohol, proving the unique role of IHF in xyl operon promoter regulation.
整合宿主因子（IHF）是一种DNA结合和弯曲蛋白，已在多种革兰氏阴性细菌中发现。在此，我们描述了恶臭假单胞菌中编码IHF两个亚基的基因的克隆、测序和功能分析。恶臭假单胞菌的ihfA和ihfB基因编码的100个氨基酸残基的多肽分别比大肠杆菌IHF亚基长1个和6个残基。恶臭假单胞菌的ihfA和ihfB基因可以有效地互补大肠杆菌ihf突变体，这表明恶臭假单胞菌的IHF亚基可以与大肠杆菌的IHF亚基形成功能性异二聚体。对大肠杆菌和恶臭假单胞菌蛋白质序列之间氨基酸差异的分析表明，在IHF的进化过程中，氨基酸变化主要局限于N端结构域和极端C端。这些变化不会干扰二聚体的形成或DNA识别。我们构建了一个携带ihfA基因敲除的恶臭假单胞菌突变株，并证明IHF对于甲苯降解上途径的木糖操纵子P（U）启动子的表达至关重要。进一步表明，携带TOL质粒的恶臭假单胞菌ihfA突变株在芳香族模型化合物苄醇的降解方面存在缺陷，证明了IHF在木糖操纵子启动子调控中的独特作用。
