The integration host factor (IHF) is a sequence-specific, histone-like, multifunctional DNA-binding and -bending protein of Escherichia coli. The characterization and functional analysis of this protein has been carried out mainly in bacteriophage lambda and other mobile genetic elements. Less is known concerning the role of IHF in E. coli, although it has been implicated in a number of processes in this organism including DNA replication, site-specific recombination, and gene expression. In this paper we report data concerning the binding of IHF protein to the recA gene region. IHF binds to at least four sites of the DNA fragment containing the recA gene, as shown by gel mobility shift assays. On the basis of the ihf consensus sequences published, we have been able to identify two sequences of putative ihf sites (ihf 1 and ihf2) into the 1390 bp long sequence containing the recA gene, but only the ihf2 site was able to bind IHF, as measured by gel mobility shift experiments. The nonfunctional ihf1 sequence was found to overlap the -35 region of the recA promoter and the functional ihf2 sequence was found within the recA gene structure at nt +780 to +807 (both with three mismatches according to the consensus sequence of Kur et al., 1989). This confirms our earlier results that the IHF-DNA interaction does not depend on any very rigid sequence, but also on the suitable sequences of the neighbouring regions, together with the proper DNA conformation.(ABSTRACT TRUNCATED AT 250 WORDS)