基因表達(dá)的調(diào)控英文課件

1、Regulation of Gene Expression基因表達(dá)的調(diào)控英文課件Section 1Principles and ConceptsSection 1Principles and Conc 1.1 ConceptsGene: A DNA segment that contains the all genetic information required to encodes RNA and protein molecules. Genome: A complete set of genes of a given species. Gene expression: A process

2、 of gene transcription and translation. 1.1 ConceptsGene: A DNA segSpecificity of gene expressionTemporal specificity (also called stage specificity): why in the infant not in the aged ones? Spatial specificity (also called tissue specificity): why in liver not in brain? Specificity of gene expressi

3、onSpecificity of gene expressionSpecificity of gene expression Type of gene expressiona. Constitutive expressionSome genes are essential and necessary for life, and therefore are continuously expressed, such as those enzymes involved in TAC. These genes are called housekeeping genes. Type of gene ex

4、pressiona. Con b. Induction and repression The expression levels of some genes fluctuate in response to the external signals. b. Induction and repression Some genes demonstrate higher expression level once being activated. It is called induced expression. On the other hand, some genes are repressed

5、and their expression levels are lower. It is called repressed expression.Some genes demonstrate higher 1.2 Regulatory ElementsGene expression is a multiple-level process. Transcription initiation is a key point of controlling gene expression. 1.2 Regulatory ElementsGene Basic elements that regulate

6、the transcription include: Special DNA sequencesRegulatory proteinsDNA-protein interaction and protein-protein interactionRNA polymerase Basic elements that regulate tFor prokaryotic systems: Operon is composed of structural genes, promoter, operator, and other regulatory sequences. a. Special DNA s

7、equenceOther requlatory sequenceOperatorPromoter Sturctural genesFor prokaryotic systems: a. Sp The DNA sequence that RNA-pol can bind to and initiate the transcription. Promoter The DNA sequence that RNA-polThe DNA sequence adjacent to the structural genes that the repressor protein can bind to and

8、 prevent the transcription of structural genes. OperatorThe DNA sequence adjacent to t Cis-acting elements is the special DNA sequence that can affect the expression of its own gene. For eukaryotic systems: Cis-acting elements is the spb. Regulatory proteinsFor prokaryotic systems: Specific factor:

9、It facilitates the binding of RNA-pol to particular DNA sequence. Repressor: It binds to the operator and prevent the transcription, known as negative regulation. b. Regulatory proteinsFor prokActivator: It associates with DNA near the initiation point, resulting in the increase of RNA-pol binding a

10、ffinity and the enhancement of the transcription efficiency. Activator: It associates withFor eukaryotic systems: The regulatory proteins are called transcription factors (TF). After expression, TF will interact with the cis-acting elements to activate another genes. Therefore, they are referred to

11、as trans-acting factors. For eukaryotic systems: Trans-acting factorsTrans-acting factorsThe regulation is implemented through numerous interactions between cis-acting elements and trans-acting factors. They are non-covalent bond. c. DNA-protein interactionsThe regulation is implemented Proteins may

12、 have to interact with each other prior to the DNA binding. Proteins can form a homo or hetero-dimer form to function properly. Present in prokaryotes as well as eukaryotes.Protein-protein interactionsProteins may have to interact Section 2Gene Regulation of Prokaryotic Systems Section 2Gene Regulat

13、ion of Common featuresProkaryotic genes are polycistron systems, that is, several relevant genes are organized together to form a transcription unit - operon. The majority of gene regulation is negative. Inducers are used to remove the repression. Common featuresProkaryotic ge Operon is a coordinate

14、 unit for the regulation.Transcription initiation is the key point for regulation. Translation can also be regulated. 2.1 Regulation of Transcription Operon is a coordinate unit fStructure of lac operonStructure of lac operonMetabolism of lactoseMetabolism of lactoseBacteria do not express these thr

15、ee enzymes when glucose is available. However, bacteria produce those enzymes if lactose is present and glucose is absent.Inducible expressionBacteria do not express these Sequence of lac operonlac operon (TTTACA/TATGTT) is a weak promoter, and has a basal expression level. CAP (Catabolite gene acti

16、vator protein) binding site is at -60 region. CAP is a homodimer with binding ability to DNA and cAMP. Sequence of lac operonlac opeGlucose inhibits the formation of cAMP. When glucose is present, cAMP is lower. Only after glucose is exhausted, cAMP becomes higher. The CAP-cAMP complex is formed, an

17、d this complex binds to the CAP binding site on lac operon. Glucose inhibits the formation When lactose is absent, no lac gene is expressed.Situation 1 When lactose is absent, no lalacI gene has its own promoter, and its expression can produce LacI repressor. The tetrameric Lac repressor binds to th

18、e lac operator site Olac.The binding blocks the RNA-pol moving on DNA template, and no lacZ, lacY, and lacA are expressed. lacI gene has its own promotergalactosidaseSituation 2When lactose is present, lacZ, lacY, and lacA genes are expressed.galactosidaseSituation 2When lThe galactosidase is weakly

19、 expressed (at the basal level). When lactose is present, it is converted to allolactose or galactose that binds to the repressor. The repressor can no longer bind to the operator, and lac gene can be expressed. Galactose , Allolastose and IPTG are referred to as inducer. The galactosidase is weakly

20、 ex Inducers Inducers The lacZYA RNA transcript is very unstable and could be degraded quickly. Therefore, the synthesis of three enzymes will be cease under normal condition. Presence of lactose The lacZYA RNA transcript is When glucose is present, the cAMP is low, no CAP-cAMP is formed and the exp

21、ression of the lac operon is still low. Situation 3 When glucose is present, the When glucose is absent and lactose is present, the CAP-cAMP complex binds to the CAP site to activate the lac gene. Situation 4 When glucose is absent and la Coordinate expressionNo glucoseGlucose Coordinate expressionN

22、o gluc 2.2 Transcription AttenuationThe trp operon is one of the constitutive genes expressed at the basal level.The structural gene of trp operon encodes 5 enzymes used for the synthesis of Trp.Trp operon 2.2 Transcription Attenuatio The trp repressor gene can be expressed, but it does not bind to

23、the operator. When Trp is more than enough, the repressor will form a complex with Trp. The complex binds to the operator, blocking the synthesis of Trp. The trp repressor gene can be Trp operon Trp operon Attenuation mechanismIn addition to the repressor regulation, trp gene has a fine tuning mecha

24、nism called attenuation. The trp operon is regulated using attenuation mechanism at the translation level. Attenuation mechanismIn addit Leader sequence Leader sequence Possible hairpins1/2 and 3/4 hairpin structure2/3 hairpinstructure Possible hairpins1/2 and 3/4 High Trp concentration High Trp con

25、centration Low Trp concentration Low Trp concentrationSection 3Regulation of Eukaryotic TranscriptionSection 3Regulation of Euka Structural featuresLarge genome: 3 x 109 bps, 35 000 genesMonocistronRepeated sequences: different lengths and different frequencies. Often inverted repeatsSplite genes: s

26、eparated by introns and exons alternatively Structural featuresLarge geno Regulation features1. RNA-pol: 3 forms (I, II, and III) for different RNAs2. Changes of chromosomal structure Hypersensitive siteBase modificationIsomer-conversionHistone changes Regulation features1. RNA-pol 3. Positive regul

27、ation4. Transcription and translation are separated5. Post-transcriptional modification6. Regulation through intercellular and intracellular signals 3. Positive regulation 3.1 Cis-acting elementsThey are specific DNA sequences, each of which regulates transcription of one or more genes. They usually

28、 have consensus sequences.Promoter: TATA box, CAAT box, and GC box, 3.1 Cis-acting elementsThey Sequence: TATAAAALocation: - 25 - 30 bpFunction: It is the binding site for TFII D, which is required for RNA polymerase binding. It controls the veracity and frequency of transcriptional initiation.TATA

29、box Sequence: TATAAAATATA boxSequence: GCCAATLocation: -70 bpFunction: It is the binding site for CTF1 (CAAT-binding transcription factor) and C/EBP (enhancer binding protein). CAAT boxSequence: GCCAATCAAT box Sequence: GGGCGGLocation: -30 -110 bpFunction: It is the binding site for a protein called

30、 Sp1. GC box Sequence: GGGCGGGC boxIt is a DNA sequence that can determine the temporal and spatial specificities of expression and increase the promoter activity. enhancerIt is a DNA sequence that can It is a negative regulation element.It will repress the transcription once interacted with specifi

31、c proteins. Silencer It is a negative regulation e 3.2. Trans-acting factorsThey are the proteins that bind indirectly to cis-acting elements and then regulate the transcription initiation.The trans-acting factors can be transcription factors (TF). 3.2. Trans-acting factorsThe transcription factorsGeneral transcription factorsSpecial transcription factorsTranscription activators EBP (enhancer binding protein)Transcription inhibitors transcription factorsGeneral General structure of TFDNA-binding domainActivation doma