Evolutionary Relationships and the TATABinding Protein

Some 2 billion to 3 billion years ago, life diverged into three lines of evolutionary descent: the eubacteria, the archaea, and the eukaryotes (see Chapter 2). Although eubacteria and archaea are superficially similar — both are unicellular and lack a nucleus—the results of studies of their DNA sequences and other biochemical properties indicate that they are distantly related. The evolutionary distinction between archaea, eubacteria, and eukaryotes is clear: however, did eukaryotes first diverge from an ancestral prokaryote, with the later separation of prokaryotes into eubacteria and archaea, or did the archaea and the eubacteria split first, with the eukaryotes later evolving from one of these groups?

Studies of transcription in eubacteria, archaea, and eukaryotes have yielded important findings about the evolutionary relationships of these organisms. The results of studies in 1994 demonstrated that archaea possess a TATA-binding protein, a critical transcription factor in all three of the eukaryotic polymerases. The binding of TBP to DNA is the first step in the assembly of the eukaryotic transcription apparatus. In earlier studies, TATA-like sequences were found in eukaryotic cells, but no such sequences have been found in eubacteria. TBP binds the TATA box in archaea with the help of another transcription factor, TFIIB, which is also found in eukaryotes but not in eubacteria.

Together these findings indicate that transcription, one of the most basic of life processes, has strong similarities in

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