Binds and compacts DNA (95 to 150 base pairs) to form nucleosome-like structures that contain positive DNA supercoils (PubMed:2377617, PubMed:7809089, PubMed:10704305, PubMed:28798133). Increases the resistance of DNA to thermal denaturation in vitro (PubMed:2377617). Homodimer and heterodimer of HmfA and HmfB (PubMed:2377617, PubMed:7809089, PubMed:10704305, PubMed:11021968, PubMed:28798133). Heterodimers may be formed primarily when cells enter stationary growth (PubMed:7809089). Dimers then assemble into higher oligomers, with the DNA wrapped around the protein core (PubMed:28798133). Higher order oligomerization of these structures can give rise to long, superhelical fibers (in vitro) (PubMed:28798133). Expression is relatively low during exponential growth, and is higher during the stationary phase. Belongs to the archaeal histone HMF family.