One of the 2 subunits of integration host factor (IHF), a specific DNA-binding protein that functions in genetic recombination as well as in transcriptional and translational control. Plays a crucial role in the lysogenic life cycle of bacteriophage lambda, as it is required not only in the recombination reaction, which inserts lambda DNA into the E.coli chromosome, but also for the synthesis of int and cI repressor, two phage proteins necessary for DNA insertion and repression, respectively. The synthesis of int and cI proteins is regulated indirectly by IHF via translational control of the lambda cII protein. Has an essential role in conjugative DNA transfer (CDT), the unidirectional transfer of ssDNA plasmid from a donor to a recipient cell. It is the central mechanism by which antibiotic resistance and virulence factors are propagated in bacterial populations. Part of the relaxosome, which facilitates a site- and strand-specific cut in the origin of transfer by TraI, at the nic site. Relaxosome formation requires binding of IHF and TraY to the oriT region, which then facilitates binding of TraI. Heterodimer of an alpha and a beta chain. Part of the relaxosome, a complex composed of plasmid-encoded TraI, TraM, TraY and host-encoded IHF bound to the F plasmid origin of transfer (oriT). Belongs to the bacterial histone-like protein family.