Class of proteins involved in regulation of transcription
A coactivator is a type of transcriptional coregulator that binds to an activator (a transcription factor) to increase the rate of transcription of a gene or set of genes.[1] The activator contains a DNA binding domain that binds either to a DNA promoter site or a specific DNA regulatory sequence called an enhancer.[2][3] Binding of the activator-coactivator complex increases the speed of transcription by recruiting general transcription machinery to the promoter, therefore increasing gene expression.[3][4][5] The use of activators and coactivators allows for highly specific expression of certain genes depending on cell type and developmental stage.[2]
Some coactivators also have histone acetyltransferase (HAT) activity. HATs form large multiprotein complexes that weaken the association of histones to DNA by acetylating the N-terminal histone tail. This provides more space for the transcription machinery to bind to the promoter, therefore increasing gene expression.[1][4]
Activators are found in all living organisms, but coactivator proteins are typically only found in eukaryotes because they are more complex and require a more intricate mechanism for gene regulation.[1][4] In eukaryotes, coactivators are usually proteins that are localized in the nucleus.[1][6]