2.4) IHF
IHF, the Integration Host Factor was first discovered as an essential factor for site-specific recombination of phage λ (Miller and Friedman, 1980). Subsequent studies have shown that IHF can act as a regulator, either transcriptionally repressing or activating targets depending on the context (Arfin et al. , 2000). IHF is involved in the control of many functions including DNA replication, recombination and cell regulation (Friedman, 1988), as well as various metabolic processes, and adaptive processes (Freundlich et al. , 1992; Arfinet al. , 2000; Reverchon et al. , 2021). IHF forms a heterodimer with two subunits encoded by ihfA and ihfB and is mainly found in Proteobacteria (Table 1 ) (Nashet al. , 1987). IHF is one of the major bacterial NAPs whose intracellular concentration changes during bacterial growth, increasing during the transition to the stationary phase (Azam and Ishihama, 1999). IHF binds DNA with significant specificity, nevertheless its binding specificity appears to depend on the intrinsic structure of DNA rather than the base composition of the DNA (Swinger and Rice, 2004; Liu, Ma and Xu, 2018). Binding of IHF can induce sharp bends in DNA, up to 160° (Dhavan et al. , 2002). This could facilitate long-range interactions and affect the DNA topology. It should be noted that IHF and HU proteins are both members of the DNABII family of DNA-binding proteins and are strikingly similar to each other in sequence and in their unique structural fold (Prieto et al. , 2012). In addition, they share some similar targets (Bonnefoy and Rouvière‐Yaniv, 1992), but interact differently with the DNA and have different roles (Prieto et al. , 2012).