Binds and compacts DNA (95 to 150 base pairs) to form nucleosome-like structures that contain positive DNA supercoils. Increases the resistance of DNA to thermal denaturation. Homodimer and heterodimer of HmfA and HmfB (PubMed:2377617, PubMed:7809089, PubMed:11021968). Forms primarily homodimers during exponential phase, and heterodimers appear when cells enter stationary phase (PubMed:7809089). Dimers then assemble into higher oligomers, with the DNA wrapped around the protein core (By similarity). Expressed at constant, high levels during exponential growth and during stationary phase. Belongs to the archaeal histone HMF family.