Gene Specific Factors Differentially Enhance Transcription Rates

The basal transcription factors increase the rate of transcription for all genes; indeed, RNA polymerase cannot bind to the promoter without them. However, not all genes should be transcribed at an equal rate all the time. Red blood cells should make lots of hemoglobin but not the digestive enzyme pepsin, while stomach lining cells should do the opposite. Differential control of gene transcription is facilitated by gene-specific transcription factors.

Hormones are an important class of molecules that regulate gene expression. A hormone is not a transcription factor itself but binds to a receptor to form a gene-specific factor. Once bound together, the hormone-receptor complex binds to DNA. Growth factors and homeotic proteins also act as gene-specific factors or form complexes that do.

The number of known gene-specific factors is currently in the low thousands and inevitably will grow as the genome becomes better known. An average gene may have several dozen specific factors involved in its regulation, giving the potential for very precise control of its expression.

Schematic diagram of a gene and its regulatory regions. TFII-D, -B, -F, -E, and -H are basal transcription factors, required for binding of RNA polymerase (pol II) to the promoter. Activators and repressors enhance or reduce the rate of gene transcription.

genome the total genetic material in a cell or organism

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