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. Author manuscript; available in PMC: 2013 May 3.
Published in final edited form as: Nature. 2012 Mar 14;483(7389):286–287. doi: 10.1038/483286a

Figure 1. Two ways of starting the synthesis of messengerRNA.

Figure 1

Promoters are sequences within genes that specify where DNA’s transcription into RNA starts. a, Some promoters have a clearly recognizable sequence, or ‘TATA box’, to which transcription factor TBP can bind to recruit the enzyme RNA polymerase (Pol) II, which synthesizes messenger RNA. These promoters can alternate between repressed and active states. In the repressed state (top), a nucleosome (protein– DNA complex) blocks the transcription start site. Transcription activator proteins can then recruit additional proteins, such as the SAGA complex, to trigger nucleosome removal, allowing access to Pol II and therefore activating transcription (bottom). b, Most promoters lack a clearly recognizable TATA box, and their expression depends on the presence of transcription factor TFIID, a complex formed by TAF proteins and TBP. Transcription activators could recruit TAFs, which, in turn, might interact with both TBP and a nucleosome to keep the transcription start site accessible.