Regulation of Transcription in Eukaryotes

This article talks about regulating transcription in eukaryotes. Controlling gene expression is far more complex in eukaryotes than it is in bacteria; but, they have the same basics. Eukaryotic gene expression is controlled at initiation of transcription. In bacteria, proteins control transcription. They bind to specific regulatory sequences and modulate the activity of RNA polymerase. The same thing happens in eukaryotes. The complex task of regulating gene expression in the many differentiated cell types of multicellular organisms is accomplished primarily by the synergy of multiple different transcriptional regulatory proteins. Packaging DNA into chromatin and modifying it by the process of methylation, transmit further levels of complexity to the control of eukaryotic gene expression.

This is a picture of a transcriptional activator. It has two independent domains.

This is a picture of a eukaryotic repressor. Some repressors block the binding of activators to regulatory sequences. While, others have active repression domains that inhibit transcription by interacting with general transcription factors. 

Gene expression in eukaryotes is regulated by transcriptional activators and repressors. Activators bind to regulatory DNA sequences and stimulate transcription. They appear to be modular proteins. So, the DNA binds and activates domains of different factors and thereby these factors can frequently be interchanged using different DNA techniques. Repressors on the other hand, bind to specific DNA sequences. I like to think of them as inhibitors. In most cases, eukaryotic repressors interfere with the binding of other transcription factors to DNA. For example, when a repressor binds near the transcription start site, it can block the interaction of RNA polymerase (or general transcription factors) with the promoter. Other repressors compete with activators for binding to specific regulatory sequences.