Answer:
A. Mediator
Explanation:
Enhancers are cis regulatory sequences which are located very far - off from promoter sequence either upstream or down stream. They are capable of showing their impact even if they located far apart from promoter and Loop/Combinatorial model best describes the mechanism of action of enhancers.
The sequence of events are mentioned as under:
(1) First of all, activator binds to the enhancer;
(2) Co-activator which is also known as mediator binds to the activator;
(3) Chromatin remodelers bind with mediator at one end and heterochromatin on the other end so as to remove histones from heterochromatin and cause decondensation;
(4) General transcription factors (GTFs) bind the promoter;
(5) RNA polymerase II binds the promoter.
The enhancer forms a loop with the help of activator and mediator to reach near at promoter. In eukaryotes, activator does not interact with RNA polymerase directly, it interacts with the help of mediator so we can say that enhancer shows it's impact through protein-protein interaction.
