transactivator

A transactivator is a protein that increases transcription of one or more genes by enhancing the activity of a promoter or enhancer. Transactivators typically have a DNA-binding domain that recognizes specific regulatory sequences and a transactivation domain that recruits components of the transcriptional machinery, including coactivators and RNA polymerase II, to boost transcription initiation or elongation.

Transactivators can be cellular transcription factors or viral proteins. In natural gene regulation, transactivators control patterns of gene expression during development, differentiation, and response to signals. They often work in combination with other factors and may influence chromatin structure through coactivators with histone acetyltransferase activity or by recruiting the Mediator complex.

Viral transactivators are well-known for hijacking host transcription. For example, HIV Tat enhances transcription elongation by recruiting P-TEFb to the viral promoter, relieving pause in transcription. The herpes simplex virus protein VP16 is a potent transactivator that activates a large number of immediate-early genes.

In biotechnology and research, engineered transactivators underlie inducible gene expression systems. Tet transactivators (tTA and rtTA) respond to tetracycline or its analogs to regulate transcription in mammalian cells. Other synthetic constructs combine DNA-binding domains (such as GAL4) with strong transactivation domains to control target genes.

Overall, transactivators are central to controlling when and how much a gene is expressed, with broad implications in biology, medicine, and biotechnology.