Activator (genetics)

A transcriptional activator is a protein (transcription factor) that increases transcription of a gene or set of genes.^[1] Activators are considered to have positive control over gene expression, as they function to promote gene transcription and, in some cases, are required for the transcription of genes to occur.^[1][2][3][4] Most activators are DNA-binding proteins that bind to enhancers or promoter-proximal elements.^[1] The DNA site bound by the activator is referred to as an "activator-binding site".^[3] The part of the activator that makes protein–protein interactions with the general transcription machinery is referred to as an "activating region" or "activation domain".^[1]

Most activators function by binding sequence-specifically to a regulatory DNA site located near a promoter and making protein–protein interactions with the general transcription machinery (RNA polymerase and general transcription factors), thereby facilitating the binding of the general transcription machinery to the promoter.^[1][2][3][4] Other activators help promote gene transcription by triggering RNA polymerase to release from the promoter and proceed along the DNA.^[2] At times, RNA polymerase can pause shortly after leaving the promoter; activators also function to allow these "stalled" RNA polymerases to continue transcription.^[1][2]

The activity of activators can be regulated. Some activators have an allosteric site and can only function when a certain molecule binds to this site, essentially turning the activator on.^[4] Post-translational modifications to activators can also regulate activity, increasing or decreasing activity depending on the type of modification and activator being modified.^[1]

In some cells, usually eukaryotes, multiple activators can bind to the binding-site; these activators tend to bind cooperatively and interact synergistically.^[1][2]