Kinase Glossary: Primordial
Primordial kinases are those that likely arose in the common ancestor of all extant eukaryotes. This is not a standard term, and defining primordial kinases is imperfect, since we don't have full sampling of extant eukaryotes, nor do we know the branching order of early evolution, or the extent of kinase loss or horizontal transfer. Our current working definition is that if a kinase is present in at least two major basal clades (unikonts, plants, excavates, chromalveolates) then it is primordial. About 17 kinases are absent from excavates but present in several other major clades: we classify these as primordial, though if excavates are the earliest-branching eukaryotic lineage (which is controversial), this may not be correct.