coactivator
noun
co·ac·ti·va·tor
| \ (ˈ)kō-ˈak-tə-ˌvā-tər
\
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Medical Definition of coactivator
: a protein or protein complex that activates genetic transcription usually by binding to a transcription factor
Gene-regulatory proteins that do not themselves bind DNA but assemble on DNA-bound gene regulatory proteins are often termed coactivators or corepressors, depending on their effect on transcription initiation.— Bruce Alberts et al., Molecular Biology of the Cell, 2002