Final answer:
Activator proteins binding to the promoter site enhance the interaction with RNA polymerase, aiding in transcription initiation, whereas repressors inhibit this process. DNA bending and enhancer regions are integral to allowing activators to contact transcription factors and RNA polymerase.
Step-by-step explanation:
When activator proteins bind to the actual promoter site, they enhance the interaction between RNA polymerase and a particular promoter. This interaction enables the RNA polymerase to more efficiently initiate the transcription of a gene. Activators often work in tandem with enhancer regions and DNA bending proteins to facilitate this process. The DNA must bend to allow the activator proteins at the enhancer sites to contact the general transcription factors and RNA polymerase at the promoter. At times, activators can directly bind to the promoter-proximal elements, such as the CAAT box or GC box, aiding in the recruitment of basal transcription factors necessary for transcription initiation.
Furthermore, gene expression can be regulated through repressor proteins, which bind to non-coding sequences on DNA, impeding the progress of RNA polymerase. In the context of transcription regulation, activators and repressors modulate the frequency and initiation of transcription, playing pivotal roles in gene expression.