HU, the major histone-like protein of E. coli, modulates the binding of IHF to oriC.

HU is one of the most abundant DNA binding proteins of bacteria. Unlike IHF, integration host factor of Escherichia coli, with which HU shares many properties, including a strong sequence homology and similar predicted structure, HU seems to bind non-specifically to DNA whereas IHF binds to specific sites. In this work we compare the binding characteristics of HU and IHF to a DNA fragment containing the minimal origin of replication of E. coli (oriC) and we analyse the effect of HU on the binding capacity of IHF to this oriC fragment. We show that HU interacts randomly and non-specifically with oriC as opposed to the specific binding of IHF to this same DNA sequence. In addition, we show that HU can modulate the binding of IHF to its specific oriC site. Depending on the relative concentrations of HU and IHF, HU is able either to activate or to inhibit the binding of IHF to oriC.