Fig. 6: Unified, multi-stage model for the functional innovations of TBP.

a Evolutionary model for the functional innovations of TBP from bacteria to vertebrates. This includes the emergence of orthogonal TBP–TFIIB system in viruses. The functional innovations range from binding double-stranded nucleic acids by a simple, single TBP-lobe unit in bacteria to becoming a hub for complex gene-expression regulation and functional diversification via TBP paralogs and N-terminal expansions in vertebrates. b Functional innovations of TBP enable it to integrate distinct regulatory signals in eukaryotes.