Figure 5.

Alternative models of transcription initiation. Cartoon model displaying the proposed regulatory factors of diffuse and focused transcription at TFIIB-bound initiation complexes. After initial recruitment of the initiation complex to a region, initiation may occur at the optimal TSS (focused initiation). Dispersed nucleosome-linked initiation may result from the presence of a transcriptionally permissive region with a downstream nucleosome serving as a boundary element. Alternatively, disperse transcription may operate in a local region resulting in a positioned downstream nucleosome.