A protein intermediary in the interaction of a hormone with the genome.

The increased rate of RNA synthesis by target cells caused by the plant hormone auxin has been studied as an example of hormonal regulation of transcription. The hormone does not interact directly with chromatin but requires a protein mediator. In the presence of this mediator, auxin increases the rate of RNA synthesis both by isolated plant nuclei and by isolated chromatin. This increased rate of RNA synthesis occurs even in the presence of saturating amounts of RNA polymerase. The hormone and protein do not affect the rate of RNA synthesis if pure DNA is used as the template. The results suggest that auxin plus the protein increase the rate of RNA synthesis by making an increased portion of the genome available for transcription.