1. Lecture12 - Based on Chapter 18 - Regulation of Gene Expression in Eukaryotes Copyright © 2010 Pearson Education Inc.

2. 1 -Levels of Control of Gene Expression in Eukaryotes

3. 11 – The Role of Chromatin in Regulating Gene Transcription

4. 12 – Gene Silencing and Genomic Imprinting

5. 13 – Gene Silencing by DNA Methylation

6. 14 – Genomic Imprinting

7. 15 – RNA Processing Control

8. 1 -Levels of Control of Gene Expression in Eukaryotes

9. 17 – RNA Interference

10. 1 -Levels of Control of Gene Expression in Eukaryotes

11. 16 – mRNA Translation Control 1.Ribosomal translational control, selecting mRNAs for translation, also has an impact on gene expression. a.Unfertilized eggs are an example, in which mRNAs show significant increases in translation after fertilization without new mRNA synthesis. b.Stored mRNAs are associated with proteins that both protect them and inhibit their translation. c.Poly(A) tails promote translation initiation, and stored mRNAs generally have shorter tails. i. In some mRNAs of mouse and frog oocytes, a normal-length poly(A) tail is added and then trimmed enzymatically. ii. Particular mRNAs are marked for deadenylation by a region in the 39 untranslated region, called the adenylate/uridylate (AU)-rich element (ARE), with the consensus sequence UUUUUAU. iii. Activation of the stored mRNA occurs when a cytoplasmic polyadenylation enzyme recognizes the ARE and adds about 150 A residues, making a full-length poly(A) tail.

12. 18 – Regulation of Gene Expression – Control of mRNA Degradation

13. 19 - Regulation of Gene Expression – Control of Protein Degradation 1.Protein regulation occurs in many ways. Examples: a.A constitutively produced mRNA may be translated continuously, and so the protein degradation rate determines its level. b.A short-lived mRNA may make a very stable protein, so that it persists for long periods in the cell. 2.Protein stability varies 3.Proteolysis (protein degradation) in eukaryotes requires ubiquitin, a protein cofactor. 4.Protein stability is directly related to the amino acid at the N terminus of the protein (the N-end rule). In yeast, stability of the same protein was measured with different N-terminal amino acids: 5.The N-terminal amino acid directs the rate of ubiquitin binding, which in turn determines the half-life of the protein. 6.To summarize, prokaryotes control gene expression mainly at the transcriptional level, while eukaryotes regulate at transcriptional, posttranscriptional, and posttranslational levels. Eukaryotic systems control: Transcription, Precursor-RNA processing, Transport from the nucleus, Degradation of mature RNAs, Translation of mRNAs, and Degradation of protein.