Evolutionary relationship of three families of the R2K ATP-grasp module shown to the left and conserved contextual associations including operonic organizations and domain architectures are provided on the right. Tree nodes supported by bootstrap >75% are shown. Proteins are denoted by their GenBank index numbers and their complete species names and colored according to their lineages: bacterial in blue, viral in green, amoeboazoan in orange, Naegleria in purple, fungal in red. Conserved gene neighborhoods are depicted as boxed, labeled arrows with the arrowhead pointing to the C-terminus of the protein. Genes known to be part of the T6SS are shaded in gray, including the “T6SS.unk” gene containing a domain of unknown function in the secretion system. Conserved domain architectures are depicted as adjoining, labeled shapes.