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transcription factor

(Science: molecular biology) protein required for recognition by rNA polymerases of specific stimulatory sequences in eukaryotic genes.

Several are known that activate transcription by rNA polymerase II when bound to upstream promoters.

transcription of the 5S rNA gene in xenopus by rNA polymerase III is dependent on a 40 kD protein TFIIIA that binds to a regulatory site in the centre of the gene and was the first protein found to exhibit the metal binding domains known as zinc fingers.