Question

If an enhancer is placed on one plasmid and its corresponding promoter is placed on a second plasmid that is catenated (linked) with the first, initiation is almost as efficient as when the enhancer and promoter are on the same plasmid. However, initiation does not occur when the two plasmids are unlinked. Explain.

Short answer

RNAP II and the transcription factor (TF) can't loop around the DNA if the two plasmids aren't linked.

Step-by-step solution

Definition of Concept

A plasmid is a type of double-stranded, circular, tiny DNA molecule that differs from a cell's chromosomal DNA.Both bacterial and certain eukaryotic cells naturally contain plasmids.

Initiation does not occur when the two plasmids are unlinked

RNAP II is stimulated to bind to specific promoters by specific TF, and once linked, it recognizes enhancers. Enhancers and promoters on the same piece of DNA are far apart, so their interaction necessitates DNA looping.

Enhancer-bound TF and promoter-bound RNAP II can interact with each other and start translation at the promoter if they are on different but linked plasmids.But in the unlinked plasmids, enhancer and RNAP II cannot interact, preventing transcription initiation.