- Catabolite activator protein
Catabolite Activator Protein or CAP is a
transcriptional activatorthat exists as a homodimerin solution, with each subunit comprising a ligand-binding domain at the N-terminus(CAPN, residues 1-138), which is also responsible for the dimerization of the protein, and a DNA-binding domainat the C-terminus(DBD, residues 139-209). Two cAMP ( cyclic AMP) molecules bind dimeric CAP with negative cooperativityand function as allostericeffectors by increasing the protein's affinityfor DNA. Cytosolic cAMP levels rise when the amount of glucosetransported into the cell is low, but lactoseis readily available.
CAP has a characteristic
helix-turn-helixstructure which allows it to bind to successive major grooves on DNA. The two helices are reinforcing each causing a 43° turn in the structure so overall causing a 94° degree turn in the DNA. [Schultz SC, Shields GC, Steitz TA (1991).
Crystal structure of a CAP-DNA complex: the DNA is bent by 90 degrees. Science. 253(5023):1001-7. PMID 1653449]
This opens the DNA molecule up, allowing
RNA polymeraseto bind and transcribe the genes involved in lactose catabolism. CAP thus enhances the expression of the lac operonwhen lactose is present but not glucose.
This requirement reflects the greater simplicity with which glucose may be metabolized in comparison to lactose. The cell "prefers" glucose, and if it is available, the lac operon is not activated, even when lactose is present.
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catabolite activator protein — catabolite activator protein. См. белок активатор катаболитных оперонов. (Источник: «Англо русский толковый словарь генетических терминов». Арефьев В.А., Лисовенко Л.А., Москва: Изд во ВНИРО, 1995 г.) … Молекулярная биология и генетика. Толковый словарь.
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