HISTONES AND CHROMATIN STRUCTURE IN HYPERTHERMOPHILIC ARCHAEA

HMf is a histone from the hyperthermophile Methanothermus fervidus. It is the archetype and most studied member of a family of archaeal hist ones that have primary sequences and three-dimensional structures in c ommon with the eukaryal nucleosome core histones and that bind and com pact DNA molecules into nucleosome-like structures (NLS). HMf preparat ions are mixtures of two similar, small (similar to 7.5 kDa) polypepti des designated HMfA and HMfB that in vivo form both homodimers and het erodimers. HMfA synthesis predominates during exponential growth but t he relative amount of HMfB increases as M. fervidus cells enter the st ationary growth phase. Analyses of homogeneous preparations of recombi nant (r) (HMfA)(2) and (rHMfB)(2) have demonstrated that these protein s have different DNA-binding and compaction properties in vitro, consi stent with different roles in vivo for the (HMfA)(2), (HMfB)(2) and HM fA . HMfB dimers, and for the NLS that they form, in regulating gene e xpression and in genome compaction and stability.