Participation of the histone-like protein HU and of IHF in minichromosomal maintenance in Escherichia coli.

The closely related Escherichia coli genes, hupA, hupB, himA and himD (hip), encode the bacterial histone-like protein subunits, HU-2, HU-1, IHF chi and IHF beta, respectively. We report here that E. coli minichromosomes [plasmids (2.7-12.2 kb) with oriC] carrying the intact mioC region were unable to transform mutants deficient in both HU and integration host factor (IHF), whereas they could transform mutants deficient in either HU or IHF as efficiently as the wild-type strain. Minichromosomes carrying a deletion of the proximal part of mioC or a DnaA box just upstream from mioC could not transform cells deficient in IHF, but could transform cells deficient in HU. These results suggested that HU and IHF participate in minichromosomal replication from oriC in E. coli.