Transcript 11GeneExpr
Regulation of Gene Expression Chapter 8 You will not be responsible for: Specific DNA binding motifs Specific examples of combinational control Patterning of Drosophila development Questions in this chapter you should be able to answer: Chapter 8- #s1 – 6, 8, 9,12,13 Gene Regulation 1 Why and when does gene regulation occur? Differentiation Development Response ‘Housekeeping’ vs Inducible genes Gene Regulation 2 Where in the flow of information from DNA to protein does regulation occur? Transcriptional Post-transcriptional (influence activation of RNA polymerase) Gene Regulation 3 What is an operon? What are the two major types of gene regulatory proteins? Repressors Activators Gene Regulation 4 How do DNA binding proteins recognize appropriate sequences? Homeodomain TATA-binding protein Zinc finger Gene Regulation Leucine zipper 5 How does a repressor protein function? The “tryptophan operon” model trp operon encodes genes for tryptophan synthesis Promoter element Operator element Repressor protein Gene Regulation 6 How does an gene activating protein function? e.g., Catabolic Activator Protein (CAP) Question 8-10 The ArgR repressor protein regulates genes involves in arginine biosynthesis by binding to promotor sequences. Would you expect that binding of Arg to the ArgR protein would increase or decrease its affinity for the regulatory sequence? Gene Regulation 7 How can gene repression and activation yield subtle regulatory control? e.g., the ‘lac operon’ Encodes genes for Lactose breakdown CAP binds cAMP high GLU = low cAMP low GLU = high cAMP Virtual Cell Animation Lac operon Gene Regulation 8 How is transcriptional control different in eukaryotes? … 3 mechanisms Remember… 1) Chromatin Remodeling DNA supercoiling Histone modifications Gene Regulation 9 Also remember… 2) General transcription factors TATA box associated RNA polymerase II associated Add to this… 3) Enhancer and silencer Elements Combinational control Gene Regulation 10 How far away from a gene can a gene enhancer function? Through genetic engineering you engineer cells with varying distance between a gene and its enhancer. For each cell line, you measure the level of mRNA expression, and get the pattern shown in this figure. A. Why does expression initially increase as the distance increases? B. Why does enhance activity oscillate ~ every 10 bases? C. Why does oscillation eventually dampen out? D. Why does enhancer activity slowly decline? Gene Regulation 11 “Epigenetic” control -- transmission of regulatory states to subsequent cell generations FEED_FORWARD GENE REGULATION 1) Feed-forward transmission of gene regulators 2) Histone modification **** see question 5-13 **** HISTONE MODIFICATION 3) Cytosine methylation -- “Genomic imprinting” Gene Regulation 12 Post-Transcriptional Control Mechanisms Function after transcription begins or is completed RNA interference Ubiquitylation proteosomes 1) Control of (alternative) exon/intron splicing 2) Riboswitches RNA 5’-UTR binding proteins 1) Allosteric regulation 2) Covalent regulation 3) etc. Gene Regulation 13 What is RNA interference “RNAi” ? Targeted degradation of mRNAs dsRNA precursors -- processed by dicer enzyme -- yield short (~21 base) RNA From exogenous sources -- yield siRNA -- protection against pathogens From endogenous -- yield miRNA -- often in introns -- gene regulation RISC -- “RNA Induced Silencing Complex -- mi/siRNA ‘guides’ it to target mRNAs Gene Regulation 14 RNA interference has many research applications Targeting of specific mRNAs Short hairpin RNAs (shRNA) shRNA libraries available Future therapeutic applications? Gene Regulation 15