Question

Describe the cis-acting elements that act as core promoter elements for RNA polymerase II transcription. Indicate the role of each element and the trans-acting factor that interacts with the element.

Answer 1

cis-acting DNA sequences that regulate RNA polymerase II transcription include the proximal promoter, enhancers, silencers, and boundary/insulator elements. These elements contain recognition sites for a variety of sequence-specific DNA-binding factors that are involved in transcriptional regulation.

• The proximal promoter is the region in the immediate vicinity of the transcription start site (roughly from −250 to +250 nt). Enhancers and silencers can be located many kbp from the transcription start site and act either to activate or to repress transcription.
• Boundary/insulator elements appear to prevent the spreading of the activating effects of enhancers or the repressive effects of silencers or heterochromatin.

Trans-acting factors, usually considered to be proteins, that bind to the cis-acting sequences to control gene expression. These factors which bind to consensus module sequences can bind to any promoter that contains the sequence. The binding of multiple factors may be essential for transcription initiation. Enhancers, which normally have a consensus 72 bp repeat sequence, have sites for multiple trans- acting factors to bind. Thus genes with enhancers may require several complexes to be constructed for gene expression to be initiated.