The promoter is a cis-acting site present physically continuous with transcription unit and provides a binding site for RNA polymerase enzyme. Enhancers are the upstream activation site present within promoter and interact with protein other than RNA polymerase thereby regulating the activity of the promoter. The operator is a DNA sequence present between the promoter region and the first coding gene. The main difference between a euchromatin and heterochromatin region lies in their DNA content; euchromatin is loosely packed DNA with higher gene concentration as compare to heterochromatin which is tightly packed and has less gene concentration, thus less DNA content. Being compactly packed with lesser DNA content, heterochromatin is not transcribed. Thus, the correct answer is option E.