Archaeal histones and the origin of the histone fold.

Histone sequences have been identified in many archaeal genomes and in environmental samples, and they constitute a family of proteins that are structural homologs of the eukaryotic core histones. Most archaeal histones conform to the single histone-fold structural models that have been described, but a few histone variants exhibit short insertions, additional domains or fusions. Interpretation of these structural variations offers clues to the steps that might have occurred during the evolution and specialization of eukaryotic core histones.