EUKARYOTE GENE REGULATION Ch 17 SOURCES OF COMPLEXITY Gene regulation in eukaryotes: MUCH more complex Larger amount of DNA Most genes of mRNAs must be spliced, capped, and polyadenylated Chromosomes in a double membrane nucleus Movement of RNAs into cytoplasm RNA stability Modulation of mRNA translation, protein processing, modification, and degradation (Figure 17.1) © 2012 Pearson Education, Inc. CHROMATIN REMODELING CHROMOSOMAL BOUNDARIES https://www.researchgate.net/figure/Functional-compartmentalization-of-the-yeastnucleus-top-PolII-transcription-domains_fig2_50304218 TRANSCRIPTION FACTORIES NUCLEOSOME MODIFICATIONS EUKARYOTE PROMOTER CORE ELEMENTS TFIIB Binding TBP Binding http://cancerres.aacrjournals.org/content/59/6/1315 PROMOTER DIVERSITY PROMOTER DIVERSITY, CONT’D Open Promoters Genes expressed constitutively Poly A/T tract instead of TATA Box PROMOTER DIVERSITY, CONT’D Covered Promoters Regulated genes Require chromatin remodeling WHAT DO TRANSCRIPTION FACTORS DO? Activators/Repressors DNA rearrangement RNA pol modification Energy Basal Transcription Factors Pre-Initiation Complex Transcription regulation requires binding of many regulatory factors to specific DNA sequences (cis-acting sequences) Cis-acting sequence is located on the same chromosome as the gene that it regulates Promoters Enhancers Silencers © 2012 Pearson Education, Inc. CIS-ACTING ELEMENTS OF THE EUKARYOTE PROMOTER A MODEL FOR CONTROL OF EUKARYOTIC TRANSCRIPTION The Sonic hedgehog (SHH) gene in humans and other mammals directs limb formation under an enhancer 1 million bp away from the SHH gene SHH is expressed in a tissue-specific fashion due to the action of two different enhancers One combination of regulatory proteins binds the brain enhancer in brain tissue, but a different combination binds the limb enhancer in developing limbs 20 TISSUE SPECIFIC ENHANCERS, CONT’D FIGURE 13.8 CONSERVATION OF ENHANCER SEQUENCES THE GAL SYSTEM: YEAST Components to transport galactose into the cell Inducible set of genes Gal 1, 2, 7, 10 import and process galactose Gal4: transcription factor Gal80: regulates Gal4 Mutation of Gal4 = loss of transcription Is Gal4 an activator or repressor? ENHANCERS AND SILENCERS • • Enhancer: DNA sequence stimulating transcription a distance away from promoter Silencer: DNA sequence with an inhibitory effect on the transcription of distant genes – Like enhancers, silencers are position and orientation independent, and they contain binding sites for transcription factors that decrease transcription. INSULATORS AND REGULATORY NEIGHBORHOODS • Insulator DNA sequence that blocks or insulates the effect of enhancers – May function by causing loops of chromatin that form interacting regions of genes and regulatory elements – • Insulators and their binding proteins: may help create “neighborhoods” of regulatory elements and genes that are able to physically interact but are insulated from regulatory elements in other neighborhoods AN INSULATOR BLOCKS THE ACTION OF AN ENHANCER ON A PROMOTER WHEN THE INSULATOR LIES BETWEEN THE ENHANCER AND THE PROMOTER. POST-TRANSCRIPTIONAL REGULATION PROGRAMMED DNA REARRANGEMENTS Gene amplification (remind me???) DNA rearrangement Fragment movement Recombination Loss ANTIBODY CRASH COURSE EXTREMELY Specific Made by B cells One antibody for One antigen Gene rearrangement in antibody genes RNA SILENCING 17.5 RNA INTERFERENCE IS AN IMPORTANT MECHANISM OF GENE REGULATION (2 OF 2) • Mechanisms of gene regulation by RNA interference RNA cleavage: RISC containing an siRNA, pair with mRNA molecules and cleavage to the mRNA − Inhibition of translation − Transcriptional silencing: altering chromatin structure − Silencer-independent degradation of mRNA − © 2012 Pearson Education, Inc. Review of RNAi Figure 17.16 START TO FINISH CHROMATIN REMODELING BINDING OF TRANSCRIPTION FACTORS RNA SPLICING RNAI
