A schematic representation of the different grades of contextual information in the rough hierarchy of their specificity. It should be kept in mind that the grades overlap to some extent. The different specific examples that have been discussed in the text are illustrated for each grade. The simplified phylogenetic profiles follow. -AE stands for present only in archaea and eukaryotes, while -ChBpE stands for present in Chlamydiae, Bordetella, and Eukaryotes but absent in other prokaryotes. PHP is the phosphoesterase domain found in the DNA polymerase III subunits and histidinol phosphatases and the H for the HhH DNA binding module. In the case of the Death domain, the potential interactions between Death domains in different proteins present in a given genome are shown. The enzymes of the aromatic amino acid biosynthesis pathway that are encoded by separate genes in bacteria but fused into a single polypeptide in yeast are shown as a case of gene fusion.