Organisms from the domain archaea-one of the three domains of life-share similarities with both bacteria and eukaryotes (1). Genomic comparisons demonstrate that bacteria and archaea share a common ancestor; eukaryotes are to date classified as being part of the archaeal branch (2-4). The archaeal domain comprises single-cellular organisms found in diverse habitats. Although archaea and bacteria have common features, such as a circular genome and the absence of a nucleus, at the genetic level archaea seem to be more related to eukaryotes. Amongst others, archaeal RNA polymerase, a key component of cellular life in all domains, is more similar to RNA polymerase from eukaryotes than bacterial RNA polymerase (5, 6). Archaeal ribosomes share their size and structural core with bacterial ribosomes, but are more similar to eukaryotic ribosomes when it comes to protein and rRNA sequence and some specific domains (7-9). Also, some cellular processes thought to be unique to eukaryotes, such as endosomal sorting and the ubiquitin system, have been identified in some archaea (10).

Chromatin proteins are found in every domain of life. Bacteria express DNA bending and DNA bridging proteins, such as HU and H-NS, to structure and functionally organize the genome and to regulate genome activity (11, 12). In eukaryotes and most archaeal lineages, histones are responsible for packaging