Regulation of gene expression in eukaryotes

This presentation deals with how gene expression is regulated in eukaryotes.

1. Regulation of Gene Expression in Eukaryotes BY: SUCHITTA . U

2. Overview of gene expression Differences between prokaryotic and eukaryotic gene expression Regulation of gene expression at transcriptional level 3.1 Promoter regions in eukaryotes 3.2 Role of transcription factors and formation of transcription bubble Enhancers Regulation of gene expression by intercellular and intracellular signals Regulation of RNA processing 6.1 Splicing and Alternative splicing Britten Davidson's model CONTENTS

3. OVERVIEW OF GENE EXPRESSION Producing protein from information in a DNA gene is a two step process Transcription Translation TRANSCRIPTION TRANSLATION

4. Outline of Gene Regulation Different cell types are from differential gene expression of an identical genome Complex regulatory mechanisms for expression of specific gene G ene expression is regulated at each step in the modification pathway from DNA RNA Protein The expression of gene is likely to be regulated at several of these levels The potential control levels are

5. Potential Control L evels for Regulation of Gene E xpression

6. Differences between prokaryotic and eukaryotic regulation of gene expression Regulation of gene expression in eukaryotes differ in three important ways from that of prokaryotes Action of gene regulatory proteins General transcription factors Packaging of the eukaryotic DNA into chromatin The control of gene expression occur at multiple stages but it is clear that in eukaryotes the majority of the regulatory genes occurs in the initiation of transcription

7. Regulation of gene expression at transcriptional level Promoter region of eukaryotes Nucleotide sequence (recognition sites) for the binding of RNA polymerase Located adjacent to the genes they regulate Binding of numerous protein factors to initiate transcription Transcription complex on promoter TATA Box sequence Genes which lack TATA box has Inr (Initiator sequence) which directs RNA polymerase to the promoter TATA BOX TATA binding protein ( TBP ) TBP associated factors (TAF’s) BINDS TO BINDS TO TFIID

8. Levels of Gene Regulation ROLE OF TRANSCRIPTION FACTORS AND FORMATION OF TRANSCRIPTION BUBBLE COMPLEX

9. Levels of Gene Regulation ROLE OF TRANSCRIPTION FACTORS AND FORMATION OF TRANSCRIPTION BUBBLE COMPLEX

10. Levels of Gene Regulation ROLE OF TRANSCRIPTION FACTORS AND FORMATION OF TRANSCRIPTION BUBBLE COMPLEX

11. Regulation of Gene Expresssion ENHANCERS CONTROL CHROMATIN STRUCTURE AND THE RATE OF TRANSCRIPTION Cis regulators : Regions of non coding DNA which regulate the transcription of nearby genes Enhancers : Increase the efficiency of transcription Interact with the transcription factors and regulatory proteins Responsible for full level transcription unlike promoters Full time and tissue specific expression of genes Alter configuration of the chromatin Bending and looping of DNA The transcription factors bring distant enhancers and their promoters into direct contact Complexes with transcription factors and polymerases DNA looping and binding of transcription factors to the enhancers

12. Levels of Gene Regulation INTRACELLULAR AND INTERCELLULAR SIGNALS Steroid hormones- Cortisol act by turning on the transcription specific set of genes Through diffusion the hormone enters the target cell It encounters the receptor molecules which is complexed with another protein Hsp82 Cortisol binds to receptor release of the receptor from Hsp82 Hormone receptor complex migrates to nucleus Binds to the DNA target sequences (hormone receptor elements) Activate the transcription Nuclear envelope Nucleus Transcriptional Activation Transcription Hormone receptor complex Cell membrane Receptor Cytoplasm Cortisol Hsp82 DNA binding site Hormonal regulation of gene expression

13. REGULATION OF RNA PROCESSING SPLICING m RNA is produced by splicing the primary transcript (pre-m RNA) Introns are spliced out and exons are joined together Eukaryotes have evolved a splicing machinery (SPLICESOME) – several protein RNA complexes called Sn RNP’s

14. REGULATION OF RNA PROCESSING ALTERNATIVE SPLICING 1 2 3 4

15. REGULATION OF RNA PROCESSING P 1 P 2 Alternative selection of promoters Alternative selection of cleavage/ polyadenylation sites P oly A P oly A Cell type specific transcription factor Genes for myosin light chain, amylase are regulated in this manner Immunoglobulin gene transcript Tropomyosin (cytoskeleton proteins) calcitonin/CGRP genes

16. ALTERNATIVE SPLICING If intron retained in coding regions- encode amino acids in frame with the nearby exon or stop codon in the reading frame will cause the protein to be non functional. Rarest mode in mammals Some exons can be excluded or included Neural cell adhesion molecules (N-CAMs), troponin-T (Muscle cells) Intron retaining model Exon cassette model

17. BRITTEN-DAVIDSON’S MODEL FOR REGULATION OF GENE EXPRESSION Hypothesis proposed by R.J. Britten and E. H. Davidson for the regulation of protein synthesis Gene battery model Four classes of sequences Producer genes : comparable to structural genes of prokaryotes (operon) Receptor site : operator sites in operon Integrator gene : c omparable to regulator gene, synthesis of an activator RNA Sensor site : only activated sensor sites can led to the regulation of the integrator genes. Hormones recognize these sensor sites Integrator and producer genes RNA synthesis Repeated numerous times Control the activity of large number of genes One sensor site control a set of structural genes : Battery , One sensor site + several integrators = transcription of several producer genes (receptor sites) The interrelationship of thee four classes of sequences in Britten-Davidson’s model Signal