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. Author manuscript; available in PMC: 2016 May 9.
Published in final edited form as: Nat Rev Genet. 2009 Mar;10(3):161–172. doi: 10.1038/nrg2522

Figure 5. Mechanistic differences between transcription initiation in budding yeast and metazoans.

Figure 5

A current model of how nucleosomes might direct start site selection in yeast, compared with metazoans is shown. Each step is also described in the main text. In step 1, the acetylation marks are recognized by bromodomain modules, which are found in many chromatin regulatory complexes, including the SAGA histone acetyltransferase complex and TFIID. In step 2, SAGA and TFIID then deliver TATA binding protein (TBP) to promoters. In step 3, TBP binds TFIIB and places it immediately downstream towards the transcription start site (TSS). In step 4, TFIIB positions RNA polymerase II (Pol II) at the promoter. The diagram for metazoans is a simplified version of that shown for yeast, in which the relationship between Pol II and the initiator (INR) is emphasized. The dashed arrows in both panels indicate sliding of Pol II before transcription initiation. Acetylation marks are indicated by green stars. The green colouring represents H2A.Z enrichment in the nucleosome array.