Eukaryotic Gene Expression

1. Eukaryotic Gene Expression

2. Transduction

3. Transformation

4. Conjugation

5. Transposition

6. Differential Gene Expression • If all cells have the same genome, how do cells become differentiated in a multicellular organism? • only ~20% genes expressed in a typical cell

7. Figure 15.7 histone acetylation vsDNA methylation • addition of methyl groups to bases of DNA • can condense chromatin and lead to reduced transcription • acetyl groups are attached to histone tails • loosens chromatin structure, promoting transcription Nucleosome Histonetails Unacetylated histones Acetylated histones

8. Epigenetics • inheritance of traits transmitted by mechanisms not directly involving the nucleotide sequence is called epigenetic inheritance • Epigenetic modifications can be reversed, unlike mutations in DNA sequence Can be passed to future generations

9. Figure 15.6a Signal Regulation of Transcription NUCLEUS Chromatin Chromatin modification:DNA unpacking involvinghistone acetylation andDNA demethylation • provide initial control of gene expression by making a region of DNA either more or less able to be transcribed DNA Gene availablefor transcription Gene Transcription Exon RNA Primary transcript Intron RNA processing Tail mRNA in nucleus Cap Transport to cytoplasm CYTOPLASM

10. Figure 15.8 Organization of a Eukaryotic Gene Poly-A signalsequence Enhancer(distal controlelements) Proximalcontrol elements Transcriptionterminationregion Transcriptionstart site Exon Intron Intron Exon Exon DNA • control elements, segments of noncoding DNA that serve as binding sites for transcription factors that help regulate transcription Upstream Down-stream Promoter Transcription Poly-Asignal Intron Intron Exon Exon Primary RNAtranscript(pre-mRNA) Exon Cleaved 3end ofprimarytranscript 5 RNA processing Intron RNA Proximal control elements are located close to the promoter Distal control elements, or enhancers, may be far away from a gene Coding segment mRNA 3 G P P P AAAAAA Stopcodon Startcodon UTR 5 Cap 5 UTR Poly-Atail 3

11. Figure 15.10-3 Promoter Activators Gene Transcription Factors DNA Distal controlelement TATA box Enhancer General transcriptionfactors DNA- bendingprotein • To initiate transcription, eukaryotic RNA polymerase requires the assistance of proteins called transcription factors • control elements must interact with specific transcription factors Group of mediator proteins RNApolymerase II RNApolymerase II Transcriptioninitiation complex RNA synthesis

12. Figure 15.10-3 Promoter Activators Gene Transcription Factors DNA Distal controlelement TATA box Enhancer General transcriptionfactors DNA- bendingprotein activator is a protein that binds to an enhancer and stimulates transcription Bound activators are brought into contact with a group of mediator proteins through DNA bending The mediator proteins in turn interact with proteins at the promoter forming transcription initiation complex Group of mediator proteins RNApolymerase II RNApolymerase II Transcriptioninitiation complex RNA synthesis

13. Transcription Factors

14. Figure 15.11 Promoter Albumin gene Enhancer Combinatorial Control of Gene Activation Controlelements Promoter Crystallin gene Enhancer (a) LIVER CELL NUCLEUS (b) LENS CELL NUCLEUS • A particular combination of control elements can activate transcription only when the appropriate activator proteins are present Availableactivators Availableactivators Albumin genenot expressed Albumin geneexpressed Crystallin genenot expressed Crystallin geneexpressed

15. Coordinately Controlled Genes in Eukaryotes • Unlike the genes of a prokaryotic operon, each of the co-expressed eukaryotic genes has a promoter and control elements • These genes can be scattered over different chromosomes, but each has the same combination of control elements • Activators recognize specific control elements and promote simultaneous transcription of the genes

16. Figure 15.12 Exons Post-Transcriptional Regulation DNA 5 2 1 3 4 • alternative RNA splicing, different mRNA molecules are produced from the same primary transcript PrimaryRNAtranscript 2 1 3 4 5 RNA splicing or mRNA 5 5 1 2 1 2 3 4

17. Figure 15.13 1 2 miRNA miRNA-proteincomplex RNA interference (RNAi) and MicroRNAs The miRNA bindsto a target mRNA. • MicroRNAs (miRNAs) are small single-stranded RNA molecules that can bind to complementary mRNA sequences • These can degrade the mRNA or block its translation mRNA degraded Translation blocked If bases are completely complementary, mRNA is degraded.If match is less than complete, translation is blocked.

19. Summary of mutant phenotypes Wild-type adult:. Wild-type worms are very active and move sinusoidally unc-22 worms: unc-22 worms tend to lie still, are often outstretched (not S-shaped), and twitch. bli-1 worm: Notice the large clear area on the side of the worm (a blister in the cuticle) dpy-10 adult: Dumpy worms are shorter and wider than wild-type rol-6 adult: Roller worms have twisted bodies and roll in circles.

20. RNAi Nova Video http://www.pbs.org/wgbh/nova/body/rnai.html

21. Hint: Huntington's disease is caused by a single autosomal dominant mutant gene. The gene produces a protein that causes brain abnormalities, which interfere with coordination, speech, and metal abilities. How do you think this technology can help with the treatment of Huntington's disease?

22. The discovery of RNAi has made it possible for researchers to switch genes on and off at will, simply by inserting double-stranded RNA into cells. It also holds the promise of allowing medical scientists to turn off the expression of genes from viruses and cancer cells, and it may provide new ways to treat and perhaps even cure diseases.

23. Regulatin’ Genes video • http://www.youtube.com/watch?v=9k_oKK4Teco