Coactivator (genetics)
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A coactivator is a protein that increases gene expression by binding to an activator (or transcription factor) which contains a DNA binding domain. The coactivator is unable to bind DNA by itself.
The coactivator increases the rate of initiation by stabilising the formation of the RNA polymerase holoenzyme enabling faster clearance of the promoter.
Some coactivators possess intrinsic histone acetyltransferase (HAT) activity, which acetylates histones and causes chromatin to relax in a limited region allowing increased access to the DNA. CBP and p300 are examples of coactivators with HAT activity.
The same coactivator will likely be used to increase transcription of many different genes, since it is the activator that provides the specificity to a particular sequence.
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