Chapter 12 Transcription Activators in Eukaryotes CopyrightThe McGraw-Hill Companies,Inc.Permission required for reproduction or display. Courtesy Nicola P.Pavletich,Sloan-Kettering Cancer Center,Science(15 July 1994)cover.Copyright AAAS
Chapter 12 Transcription Activators in Eukaryotes
12.1 Categories of Activators(激活因子) Activators (gene-specific TF)can stimulate or inhibit transcription by RNA polymerase ll Structure is composed of at least 2 functional domains(功能域) - DNA-binding domain(DNA结合域) -Transcription-activation domain(转录激活域) - Many also have a dimerization domain(二聚 作用域) 12-2
12-2 12.1 Categories of Activators (激活因子) ✓ Activators (gene-specific TF) can stimulate or inhibit transcription by RNA polymerase II ✓ Structure is composed of at least 2 functional domains (功能域) – DNA-binding domain (DNA结合域) – Transcription-activation domain (转录激活域) – Many also have a dimerization domain (二聚 作用域)
DNA-Binding Domains √Protein domain(蛋白质结构域)isan independently folded region of a protein DNA-binding domains have DNA-binding motif (DNA结合基序) -Part of the domain having characteristic shape specialized for specific DNA binding -Most DNA-binding motifs fall into 3 classes 1.Zinc-Containing Modules(含锌组件) 2.Homeodomains(同源域) 3.bZIP and bHLH Motifs(Bzip和bHLH基序) 12-3
12-3 DNA-Binding Domains ✓ Protein domain (蛋白质结构域) is an independently folded region of a protein ✓ DNA-binding domains have DNA-binding motif (DNA结合基序) – Part of the domain having characteristic shape specialized for specific DNA binding – Most DNA-binding motifs fall into 3 classes 1. Zinc-Containing Modules (含锌组件) 2. Homeodomains (同源域) 3. bZIP and bHLH Motifs (Bzip和bHLH基序)
Zinc-Containing Modules There are at least 3 kinds of zinc-containing modules that act as DNA-binding motifs All use one or more zinc ions to create a shape to fit an a-helix of the motif into the DNA major groove -Zinc fingers(锌指)：TFlA,Sp1 -Zinc modules(锌组件)：nuclear receptor -Modules containing 2 zinc and 6 cysteines (含两个锌离子和六个半胱氨酸组件)：GAL4 12-4
12-4 Zinc-Containing Modules ✓ There are at least 3 kinds of zinc-containing modules that act as DNA-binding motifs ✓ All use one or more zinc ions to create a shape to fit an a-helix of the motif into the DNA major groove – Zinc fingers (锌指): TFII A,Sp1 – Zinc modules (锌组件):nuclear receptor – Modules containing 2 zinc and 6 cysteines (含两个锌离子和六个半胱氨酸组件):GAL4
Homeodomains These domains contain about 60 amino acids Resemble the helix-turn-helix proteins in structure and function Found in a variety of activators Originally identified in homeobox proteins (同源盒蛋白)regulating fruit fly development 12-5
12-5 Homeodomains ✓These domains contain about 60 amino acids ✓Resemble the helix-turn-helix proteins in structure and function ✓Found in a variety of activators ✓Originally identified in homeobox proteins (同源盒蛋白) regulating fruit fly development
bZIP and bHLH Motifs A number of transcription factors have a highly basic DNA-binding motif linked to protein dimerization motifs -Leucine zippers -Helix-loop-helix Examples include: -CCAAT/enhancer-binding protein -MyoD protein 12-6
12-6 bZIP and bHLH Motifs ✓ A number of transcription factors have a highly basic DNA-binding motif linked to protein dimerization motifs – Leucine zippers – Helix-loop-helix ✓Examples include: – CCAAT/enhancer-binding protein – MyoD protein
Transcription-Activating Domains Most activators have one of these domains, Some have more than one These domains fall into three classes: - Acidic domains(酸性域)such as yeast GAL4 with 11 acidic amino acids out of 49 amino acids in the domain Glutamine-rich domains(谷酰胺富含域) include Sp1 having 2 that are 25%glutamine Proline-rich domains(脯氨酸富含域)such as CTF which has a domain of 84 amino acids, 19 proline 12-7
12-7 Transcription-Activating Domains ✓ Most activators have one of these domains, Some have more than one ✓ These domains fall into three classes: – Acidic domains (酸性域) such as yeast GAL4 with 11 acidic amino acids out of 49 amino acids in the domain – Glutamine-rich domains (谷酰胺富含域) include Sp1 having 2 that are 25% glutamine – Proline-rich domains (脯氨酸富含域) such as CTF which has a domain of 84 amino acids, 19 proline
12.2 Structures of the DNA-Binding Motifs of Activators DNA-binding domains have well-defined structures √X-ray crystallographic(X射线晶体衍射)studies have shown how these structures interact with their DNA targets √Interaction domains forming dimers(二聚体)， or tetramers(四聚体)，have also been described Most classes of DNA-binding proteins can't bind DNA in monomer form 12-8
12-8 12.2 Structures of the DNA-Binding Motifs of Activators ✓ DNA-binding domains have well-defined structures ✓ X-ray crystallographic (X射线晶体衍射) studies have shown how these structures interact with their DNA targets ✓ Interaction domains forming dimers (二聚体), or tetramers (四聚体), have also been described ✓ Most classes of DNA-binding proteins can’t bind DNA in monomer form
Zinc Fingers Described by Klug in TFIIIA Nine repeats of a 30-residue element: -2 closely spaced cysteines(半胱氦 followed 12 amino acids later by 2 closely spaced histidines(组氨酸) -Rich in zinc,enough for 1 zinc ion per repeat -Each zinc ion is complexed by 2 cysteines and 2 histidines in each repeat to form the finger-shaped structure or domain -Specific recognition between the zinc finger and its DNA target occurs in the major groove 12-9
12-9 Zinc Fingers ✓Described by Klug in TFIIIA ✓Nine repeats of a 30-residue element: –2 closely spaced cysteines (半胱氨 酸) followed 12 amino acids later by 2 closely spaced histidines (组氨酸) –Rich in zinc, enough for 1 zinc ion per repeat –Each zinc ion is complexed by 2 cysteines and 2 histidines in each repeat to form the finger-shaped structure or domain –Specific recognition between the zinc finger and its DNA target occurs in the major groove Zn
Arrangement of Three Zinc Fingers in a Curved Shape he McGraw-Hill Companies,Inc.Permission required fo roduction or display The zinc finger is Third finger composed of: An antiparallel B-strand Second contains the 2 cysteines finger 2 histidines in an a-helix Helix and strand are coordinated to a zinc ion First finger 6 12-10
12-10 Arrangement of Three Zinc Fingers in a Curved Shape The zinc finger is composed of: – An antiparallel b-strand contains the 2 cysteines – 2 histidines in an a-helix – Helix and strand are coordinated to a zinc ion