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11 주차 수업자료

11 주차 수업자료. Chapter 17. Regulation of Transcription in Eukaryotes. Accessibility of eukaryotic genes. Specific transcription factors. Respond to stimulus (signals) Enter nucleus Recognize and bind DNA Make contact with transcription machinery DNA-binding domain + activator domain.

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11 주차 수업자료

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  1. 11주차 수업자료

  2. Chapter 17. Regulation of Transcription in Eukaryotes

  3. Accessibility of eukaryotic genes

  4. Specific transcription factors • Respond to stimulus (signals) • Enter nucleus • Recognize and bind DNA • Make contact with transcription machinery • DNA-binding domain + activator domain

  5. Mediator for transcriptional activation • Signal: activator/repressor  mediator complex (20 protein subunits)  RNA polymerase II

  6. Enhancer and insulator • Insulator binding protein (IBP, Zn-finger protein, e.g., CTCF, CCCTC-binding factor) binds insulator sequence (GC-rich, also called boundary element) • Function of IBP can be regulated by methylation of CG sequence in insulator

  7. Matrix attachment region (MAR) • DNA binding site on nuclear matrix (or chromosomal scaffold) protein • AT-rich • Loop domain between MAR

  8. Negative regulation • Prevent binding of activator: CDP (CAAT-displacement protein) prevents binding of CTF (CAAT-binding factor) • MyoD (bHLH protein, for muscle differentiation): need to form heterodimer with other bHLH-containing protein (E-protein) for DNA binding

  9. Eukaryotic gene expression control by DNA structure

  10. Chromatin, nucleosome, and histone • Heterochromatin (condensed DNA, dark red): RNA polymerase cannot access to the promoter  no transcription • Histone acetylation  nucleosome disaggregation  gene expression

  11. Histone acetylation and chromatin remodeling • Histone acetylation by HAT (histone acetyl transferase, co-activator) • Histone deacetylation by HDAC (histone deacetylase, co-repressor) • Chromatin remodeling complex • required for access to DNA: sliding nucleosome along DNA  remodeling nucleosome into looser structure • Swi/Snf (switch sniff) binds to DNA • ISWI (imitation switch) binds to histones

  12. Eukaryotic gene activation - sequence • Binding of transcription factor (TF) to DNA • Sliding and remodeling of nucleosome by chromatin remodeling complex • Binding of HAT to TF • Acetylation of histone by HAT and loosening of nucleosome structure • Binding of other TFs to DNA • Binding of RNA pol to DNA • For transcription initiation, positive signal is required activator  mediator  RNA pol

  13. Histone modifications

  14. Regulation of eukaryotic gene expression by methylation • CG island (or CpG island) • Housekeeping gene: CG island non-methylated • Tissue-specific genes: CG island non-methylated in particular tissues where gene is expressed • Gene silencing by methylation: involves MeCP (methylcytosine-binding protein) and HDAC

  15. Genetic imprinting by methylation • Imprinting: • expression of genes in a parent-of-origin specific manner • Independent of Mendelian inheritance • Paternal: IGF-II • Maternal: IGF-IIR

  16. X-chromosome inactivation • X-inactivation: controlled by methylation of Xist gene • Expression of Xist gene  Xist RNA (non-translated)  coating and inactivation of X-chromosome by methylation (except for Xist gene)  heterochromatin (highly condensed, Barr body)

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