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^ GAL4 stimulates the transcription of galactose-metabolizing genes.

Transcription of genes not stimulated

Protein

Transcription of genes stimulated

416.22 Transcription is activated by GAL4 in response to galactose. GAL4 binds to the UASG site and controls the transcription of genes in galactose metabolism.

tor, transcription is stimulated, but, if a repressor occupies that site, no activation occurs. Alternatively, a repressor may bind to sites near an activator site and prevent the activator from contacting the basal transcription apparatus. A third possible mechanism of repressor action is direct interference with the assembly of the basal transcription apparatus, thereby blocking the initiation of transcription.

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