Catabolite activator protein

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Lac operon. (Catabolite Activator Protein is labeled "cAMP activator protein.")

Catabolite Activator Protein or CAP is a transcriptional activator that exists as a homodimer in solution, with each subunit comprising a ligand-binding domain at the N-terminus (CAP^N, residues 1-138), which is also responsible for the dimerization of the protein, and a DNA-binding domain at the C-terminus (DBD, residues 139-209). Two cAMP (cyclic AMP) molecules bind dimeric CAP with negative cooperativity and function as allosteric effectors by increasing the protein's affinity for DNA. Cytosolic cAMP levels rise when the amount of glucose transported into the cell is low, but lactose is readily available.

CAP has a characteristic helix-turn-helix structure 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.^[1]

This opens the DNA molecule up, allowing RNA polymerase to bind and transcribe the genes involved in lactose catabolism. CAP thus enhances the expression of the lac operon when 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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MeSH Catabolite+Activator+Protein}

[edit] References

^ 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

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Transcription factors and intracellular receptors

(1) Basic domains

(1.1) Basic leucine zipper (bZIP)	Activating transcription factor (AATF, 1, 2, 3, 4, 5, 6, 7) • AP-1 (c-Fos, FOSB, FOSL1, FOSL2, c-Jun, JUNB, JUND) • BACH (1, 2) • BATF • BLZF1 • C/EBP (α, β, γ, δ, ε, ζ) • CREB (1, 3, L1) • CREM • DBP • DDIT3 • GABPA • HLF • MAF (B, F, G, K) • NFE (2, L1, L2) • NRL • NRF1 • XBP1

(1.2) Basic helix-loop-helix (bHLH)	ATOH1 • AhR • AHRR • ARNT • ASCL1 • BHLHB2 • BMAL (ARNTL, ARNTL2) • CLOCK • EPAS1 • HAND (1, 2) • HES (5, 6) • HEY (1, 2, L) • HES1 • HIF (1A, 3A) • ID (1, 2, 3, 4) • LYL1 • MXD4 • MYCL1 • MYCN • Myogenic regulatory factors (MyoD, Myogenin, MYF5, MYF6) • Neurogenins • NeuroD (1, 2) • NPAS (1, 2, 3) • OLIG (1, 2) • Scleraxis • TAL1 • Twist • USF1

(1.3) bHLH-ZIP	MAX • MITF • MNT • MLX • MXI1 • Myc • SREBP (1, 2)

(1.6) Basic helix-span-helix (bHSH)	AP-2

(2) Zinc finger
DNA-binding domains

(2.1) Nuclear receptor (Cys₄)	subfamily 1 (Thyroid hormone (α, β), CAR, FXR, LXR (α, β), PPAR (α, β/δ, γ), PXR, RAR (α, β, γ), ROR (α, β, γ), Rev-ErbA (α, β), VDR) • subfamily 2 (COUP-TF (I, II), Ear-2, HNF4 (α, γ), PNR, RXR (α, β, γ), Testicular receptor (2, 4), TLX) • subfamily 3 (Steroid hormone (Estrogen (α, β), Estrogen related (α, β, γ), Androgen, Glucocorticoid, Mineralocorticoid, Progesterone)) • subfamily 4 NUR (NGFIB, NOR1, NURR1) • subfamily 5 (LRH-1, SF1) • subfamily 6 (GCNF) • subfamily 0 (DAX1, SHP)

(2.2) Other Cys₄	GATA (1, 2, 3, 4, 5, 6) • MTA (1, 2, 3)

(2.3) Cys₂His₂	ATBF1 • BCL(6, 11A, 11B) • CTCF • E4F1 • EGR (2, 3) • ERV3 • General transcription factors (TFIIA, TFIIB, TFIID, TFIIE, TFIIF: 1, 2, TFIIH: 1, 2, 4, 2I, 3A, 3C1, 3C2) • GFI1 • GLI-Krüppel family (1, 2, 3, YY1) • HIC (1, 2) • HIVEP (1, 2, 3) • IKZF (1, 2, 3) • ILF (2, 3) • KLF (2, 4, 5, 6, 9, 10, 11, 12, 13) • MTF1 • MYT1 • OSR1 • Sp1 • zinc finger ((3, 7, 9, 10, 19, 22, 24, 33B, 34, 35, 41, 43, 44, 51, 74, 143, 146, 148, 165, 202, 217, 219, 238, 239, 259, 267, 268, 281, 295, 318, 330, 346, 350, 365, 366, 384, 451, 452, 471, 593, 638, 649, 655) • Zbtb7 (7A) • ZBT (16, 17, 33)

(2.4) Cys₆	HIVEP1

(2.5) Alternating composition	AIRE • DIDO1 • GRLF1 • ING (1, 2, 4) • JARID (1A, 1B, 1C, 1D, 2) • JMJD1B

(3) Helix-turn-helix
domains

(3.1) Homeo domain	ARX • CDX (1, 2) • CRX • CUTL1 • DLX (3, 4, 5) • EMX2 • EN (1, 2) • FHL (1, 2, 3) • HESX1 • HHEX • HLX • Homeobox (A1, A3, A4, A5, A7, A9, A10, A11, A13, B1, B2, B3, B4, B5, B6, B7, B8, B9, B13, C4, C5, C6, C8, C9, C10, C11, C13, D1, D3, D4, D8, D9, D10, D11, D12, D13) • HOPX • MEIS (1, 2) • MEOX2 • MNX1 • MSX (1, 2) • NANOG • NKX (2-1, 2-5, 3-1) • PHF (3, 6, 10, 17) • POU domain (PIT-1, BRN-3: 1, 2, Octamer transcription factor: 1, 2, 3/4, 6, 7) • OTX (1, 2) • PDX1

(3.2) Paired box	PAX (1, 2, 3, 4, 5, 6, 7, 8, 9)

(3.3) Fork head / winged helix	E2F (1, 2, 3, 4, 5) • FOX proteins (C1, C2, E1, G1, H1, K2, L2, M1, N3, O1A, , O3A, O4, P1, P2, P3)

(3.4) Heat Shock Factors	HSF (1, 2, 4)

(3.5) Tryptophan clusters	ELF (4, 5) • EGF • ELK (1, 3, 4) • ERF • ERG • ETS (1, 2) • ETV (1, 4, 5, 6) • FLI1 • Interferon regulatory factors (1, 2, 3, 4, 5, 6, 7, 8) • MYB • MYBL2

(3.6) TEA domain	transcriptional enhancer factor 1, 2

(4) β-Scaffold factors with
minor groove contacts

(4.1) Rel homology region	NF-κB (NFKB1, NFKB2, REL, RELA, RELB) • NFAT (C1, C2, C3, C4, 5)

(4.2) STAT	STAT (1, 2, 3, 4, 5, 6)

(4.3) p53	p53

(4.4) MADS box	Mef2 (A, B, C, D) • SRF

(4.7) High mobility group	HNF (1A, 1B) • LEF1 • SOX (2, 3, 4, 5, 6, 8, 9, 10, 11, 13, 15, 18) • SRY • SSRP1

(4.10) Cold-shock domain	CSDA, YBX1

(4.11) Runt	CBF (CBFA2T2, CBFA2T3, RUNX1, RUNX2, RUNX3, RUNX1T1)

(0) Other
transcription factors

(0.2) HMGI(Y)	HMGA (1, 2) • HBP1

(0.3) Pocket domain	Rb • RBL1 • RBL2

(0.5) AP-2/EREBP-related factors	Apetala 2 • EREBP • B3

(0.6) Miscellaneous	ARID (1A, 1B, 2, 3A, 3B, 4A) • CAP • IFI (16, 35) • MLL (2, 3, T1) • MNDA • NFI (A, B, C, X) • NFY (A, B, C) • Rho/Sigma • R-SMAD