Gene Expression Dr. Kevin Ahern

Gene Expression

Controls on Protein Levels Gene Expression Controls on Protein Levels Transcription Splicing Polyadenylation mRNA Stability Translation Protein Stability

Transcription Control - Prokaryotic Promoter

Transcription Control - Prokaryotic Promoter Polycistronic Message in Prokaryotes

Transcription Control - Prokaryotic Promoter Allo-Lactose Lactose

Transcription Control - Prokaryotic Promoter

Transcription Control - Prokaryotic Promoter

Transcription Control - Prokaryotic Promoter CAP cAMP CAP Site of DNA

Transcription Control - Prokaryotic Promoter From Wikimedia Commons

Prokaryotic Transcription Control - Termination/Attenuation From Wikimedia Commons

Prokaryotic Transcription Control - Termination/Attenuation

Transcription/Translation Control - Riboswitches Cis-acting sequences Anti-terminator Terminator

Transcription/Translation Control - Riboswitches Lysine Bound to Riboswitch

Eukaryotic Gene Expression Much More Complexity Chromatin Many Transcription Factors Enhancers

Transcriptional Control - Eukaryotes

Increasing Magnification RNA Eukaryotic Gene Expression - Chromatin Chromatin is the Complex of DNA, Protein, and RNA Comprising Eukaryotic Chromosomes For RNA Polymerase to Perform Transcription, Access Must Be Gained to the DNA Increasing Magnification

RNA Eukaryotic Gene Expression - Epigenetics

RNA A Nucleosome is a Fundamental Unit of Chromatin Structure Eukaryotic Gene Expression - Chromatin A Nucleosome is a Fundamental Unit of Chromatin Structure Contains Two Copies Each of Four Histone Proteins - H2a, H2B, H3, and H4 DNA is Wrapped Around this Octet Core and Histone H1 is on the Outside

RNA Eukaryotic Gene Expression - Chromatin Histone Proteins Are Rich in Basic Amino Acids, Making Them Positively Charged The Positively Charged Proteins Are Attracted Strongly to the Negatively Charged Phosphates of the DNA Chemical Modifications That Affect These Charges Influence Transcription

RNA Eukaryotic Gene Expression - Chromatin

Chemical Modification RNA Eukaryotic Gene Expression - Chromatin Histone Acetyl Transferases (HATs) Use Acetyl-CoA to Put Acetyl Groups on Lysines in Histones This Neutralizes Their Positive Charge and Loosens Interactions With the Histones, Facilitating “Remodeling” or Restructuring of Chromatin to Allow Transcription to Occur Acetylated Lysines Can Also be Binding Targets for Proteins Affecting Transcription Chemical Modification Unwinding of Complex

RNA Eukaryotic Gene Expression - Epigenetics

Transcription Complex RNA Eukaryotic Gene Expression - Chromatin Histone Acetylation Favors Euchromatin and Stimulates Transcription Histone De-Acetylases Reverse These Effects, Favoring Heterochromatin and Gene Silencing The Sirtuin 1 deacetylase in humans down-regulated with insulin resistance Numerous Chemical Modifications are Made to Histone Proteins Acetylation / Deacetylation Methylation / Demethylation Phosphorylation / Dephosphorylation Ubiquitination Chemical Modification to Bases in DNA Can Also Affect Transcription Open and Accessible to Transcription Complex Condensed and Not Accessible

RNA Eukaryotic Gene Expression - Epigenetics

Epigenetics Chemical Modifications in Histones and DNA Can Cross Generational Barriers Transcriptional Effects Can Thus Be Transmitted From Parent to Progeny Independent of the Sequence of the DNA. Such Influences are Called Epigenetic

Epigenetics Överkalix study Patterns of modification of chromosomes cross generational barriers. Genetic Imprinting Överkalix study 1. A greater body mass index (BMI) at 9 years in sons, but not daughters, of fathers who began smoking early. 2. The paternal grandfather's food supply was only linked to the mortality RR of grandsons and not granddaughters. 3. The paternal grandmother's food supply was only associated with the granddaughters' mortality risk ratio. The estimation of the percentage of human genes subject to parental imprinting is approximately one to two percent, currently parental imprinting has been identified in fewer than 100 distinct named genes.

Transcriptional Control - Eukaryotes Methylation of CpG sequences in eukaryotes inhibits transcription

Transcriptional Control - Eukaryotes

Transcriptional Control - Eukaryotes

RNA Blocking Insulators Allows Enhancer to Activate Transcription Eukaryotic Gene Expression - Transcription Blocking Insulators Allows Enhancer to Activate Transcription Insulators Can Block Enhancer’s Activation of Transcription

Iron Transfer & Storage Ferritin - Cellular Protein to Bind Iron Transferrin Receptor - Membrane Protein to Transfer Iron

Iron Transfer & Storage Iron Response Element Binding Protein (IRE-BP) Iron Response Element (IRE)

Iron Transfer & Storage - Translation Regulation

Iron Transfer & Storage - mRNA Stability

RNA RNA Interference RNA Interference is a Powerful Means of Controlling Gene Expression Viral and Endogenous Cellular Genes Are Targets A Similar System Called piRNA (piwi RNA) Protects Against Transposon Genes Considerable Interest in Using Technique to Genetically Transform Organisms for Protect Against Pathogens

RNA Cellular Source Cellular Pre-Processing RNA Interference Transcription Double-Stranded RNA is Stimulus Processing Viral Infection 20 bp pieces RISC RISC Target Complementary Sequences in mRNAs

+ + RNA Complementary Sequences Align Argonaute Activity RNA Interference Complementary Sequences Align RISC RISC + Argonaute Activity in RISC Breaks mRNA, Stops Translation mRNA Translation of mRNA Stopped RISC +

RNA Protection Against Invading Viruses Stimulated by dsRNA RNA Interference Protection Against Invading Viruses Stimulated by dsRNA miRNA (cellular) & siRNA (foreign) Cellular piwi RNAs (piRNA) have similar functions in silencing transposons Widespread in Eukaryotes Actions referred to as RNA Interference (RNAi) RNA Interference Operates Through the Silencing of Gene Expression DS RNA induces Dicer to chop it into 20 BP Pieces These siRNAs/miRNAs bind to the RNA Induced Silencing Complex (RISC) One Strand is Destroyed and One Retained to Bind to Complementary mRNA sequences RISC Nuclease Activity (Argonaute) 1. Destroys mRNA Where Strand Binds or 2. siRNA/miRNA strand on mRNA blocks translation or 3. si/RNA/miRNA strand destabilizes mRNA and Targets for Destruction

RNA Bonding to mRNA Premature Stopping of Translation Degradation of RNA Interference Bonding to mRNA Premature Stopping of Translation Degradation of mRNA