Archaeal Chromatin Organization

In the light microscope, archaea resemble bacteria, in that they are small, generally single-celled organisms devoid of overt subcellular organization. Their genomes (which range in size from 0.5 to ∼6 Mb) are found in condensed nucleoid structures, rather than within nuclei and so the archaea can be broadly classified as “prokaryotes”. As in bacteria, a complex variety of proteins appear to play roles in compacting archaeal nucleoid structures. However, despite the organisational similarity between bacterial and archaeal subcellular features, archaeal nucleoid-associated proteins have intriguing parallels with the proteins that shape eukaryotic chromatin. These similarities manifest themselves both at the physical level, in the form of the structural orthology of some eukaryotic and archaeal histone proteins, and at the conceptual level, in the role of covalent modifications in modulating the DNA binding mode of archaeal chromatin proteins.