TAFs: guilt by association?

Transcription is a key step in the regulation of gene expression. Activation of transcription requires that RNA polymerase both receive regulatory signals from promoter-specific activators and initiate transcription at the correct locations in the genome, the promoters. In prokaryotes, these tasks can be accomplished through the action of σ, a factor that associates with the core RNA polymerase, directs it to promoters, and serves as a target for regulatory factors. In eukaryotes, each of the three different RNA polymerases—I, II, and III—relies on distinct sets of general factors to perform these functions. One of the general factors utilized by RNA polymerase II that shares many of the properties of σ is TFIID, a protein complex consisting of the TATA box–binding protein TBP and TBP-associated factors called TAFs