Fig 4.

Phylogenetic analysis of RibB, RibBA, and RibBX. The diagram shows the unrooted maximum likelihood phylogeny of RibB, RibBA, and RibBX protein sequences from the NCBI database. Named phyla are well supported (>80% bootstrap support, most with >90% support), while short branches render little support for any branching order deep in the phylogeny. RibBX (brown) and RibB (blue) were derived from the ancestral RibBA protein (red). RibBX evolved independently at least twice in the Proteobacteria, as denoted by superscript numbers. Deletion of RibA or the RibBX-CTD to yield RibB occurred multiple times (red lines changing to blue), most notably in the archaeal, fungal, actinobacterial, and proteobacterial lineages.