REGULATION OF GENE EXPRESSION IN EUKARYOTES

SUBMITTED TO : SUBMITTED BYMs: SHRADDHA GOSWAMI BRAJBALA MISHRA BIOTECHNOLOGY DEPARTMENT MSC II SEM

Contents

Introduction of Regulation of Gene Expression in Eukaryotes .

Cis-acting elements , Chromatin Organization & regulation at the level of processing of transcripts.

RNA-Editing ,Gene Alteration,DNA Methylation ,Regulation of gene expresson by hormone & Regulation of gene at translational level.

INTRODUCTION

Objectives Know the different levels at which gene

expression is regulated in eukaryotes, and understand the principles of regulation at each level.

Understand the functional difference between promoters and enhancers.

Understand the basics of tissue-specific gene regulation.

Eukaryotic Gene Expression  Gene Expression :- “Gene expression" covers the entire process

from transcription through protein synthesis

Eukaryotes have more complex means to regulate gene expression, because they have compartments (e.g., nucleus) within cells, and often multicellular structures that require differentiation of cells.

.

Eukaryotic Gene Regulation

Genome (amplification or rearrangement of DNA segments, chromatin remodeling: decondensation/ condensation and DNA methylation).

Transcription. Processing (and nuclear

export) of RNA. Translation (and targeting) of

protein. Posttranslational events

(folding and assembly, cleavage, chemical group modifications and organelle import/secretion).

Degradation of mRNA and proteins

Proximal elements of promoter

in prokaryote: -35 region

in eukaryote: CAAT-box, GC-box

UPE: upstream promoter element

UAS: upstream activating sequence

(2) Terminator

A DNA sequence just downstream of the coding

segment of a gene, which is recognized by RNA

polymerase as a signal to stop transcription.

(3) Enhancer

A regulatory DNA sequence that greatly

enhances the transcription of a gene.(4) Silencer

A DNA sequence that helps to reduce

or shut off the expression of a nearby

gene.

Chromatin Organization

Two forms of chromatin o Euchromatin – A lesser coiled

transcriptionally active region which can be easily accessed by the RNA polymerase

o Heterochromatin – A highly condensed transcriptionally inactive region. The genes in this region cannot be accessed by the RNA polymerases for active transcription

Chromatin remodeling

Differentchromatin remodeling complexes

disruptand reform nucleosomes. The same complex might catalyze

both reactions. The DNA-binding proteins could be involved in gene

expression, DNA replication, or DNA repair.

Chromatin Structure

Transcription Regulation

Genes are nearly always transcribed individually3 RNA Polymerases occur, requiring multiple proteins to initiate transcription

Typical eukaryotic promoter: recognition sequence + TATA box + transcription factors -> RNA Polymerase II attachment -> transcription

Transcription Regulation

RNA polymerase interacts w/promoter, regulator sequences, & enhancer sequences to begin transcription– Regulator proteins bind to regulator

sequences to activate transcription Found prior to promoter

– Enhancer sequences bind activator proteins

Typically far from the gene Silencer sequences stop

transcription if they bind with repressor proteins

Transcription Regulation Con’t

If eukaryotic genes are typically ‘alone’, to regulate expression of several.

Conserve regulatory sequences!

RNA Editing

RNA editing is a molecular process through which some cells can make discrete changes to specific nucleotide sequences within a RNA molecule after it has been generated by RNA polymerase

RNA editing is relatively rare, and common forms of RNA processing (e.g. splicing, 5'-capping and 3'-polyadenylation) are not usually included as editing. Editing events may include the insertion, deletion, and base substitution of nucleotides within the edited RNA molecule.

RNA editing occurs in the cell nucleus and cytosol, as well as within mitochondria and plastids.

RNA editing has been observed in some tRNA, rRNA, mRNA and miRNA molecules of eukaryotes and their viruses, but has not been seen in prokaryotes

RNA –editing Funtions

RNA –Editing Process

Gene Alteration

chromosomes may alter abnormally - this is said to be a: mutation. It causes miscoded mRNA

Genetic engineering alters the genetic makeup of an organism using techniques that remove heritable material or that introduce DNA prepared outside the organism either directly into the host or into a cell that is then fused or hybridized with the host

DNA-Methylation

DNA methylation involves the addition of a methyl group to the 5 position of the cytosine pyrimidine ring or the number 6 nitrogen of the adenine purine ring

In addition, DNA methylation suppresses the expression of viral genes and other deleterious elements that have been incorporated into the genome of the host over time. 

DNA -Methylation

The attachment of methyl groups (-CH3) to DNA bases after synthesis

Inactive DNA is generally highly methylated compared to DNA that is actively transcribed– The same genes in different tissues are

more heavily methylated in cells where they are not expressed

– Demethylating inactive genes can turn them on

May determine long term inactivation of genes

Methylation patterns are passed on, preserving a record of embryonic development– May account for genomic imprinting in

mammals– Methylation permanantly turns off either

the maternal or paternal allele of some genes

The role of methylation in Gene Expression

 role in repressing gene expression, perhaps by blocking the promoters at which activatingtranscription factors should bind

 proper DNA methylation is essential for cell differentiation and embryonic development.

Regulation of gene expression by

hormone Hormone affect th eregulation of

gene expression in one of two ways.

Steroid Hormones : A group of hydrophobic hormones that are derivatives of cholesterol.The effect of steriod hormones in eukaryotic regulatory proteins by direct interaction with molecular signals.

Mechanism of hormones in gene regulation.Steroid hormones enters,its target cells

&combine with a receptor protein

The hormones/receptor complex bind to a hormones response element in the DNA

The bound complex stimulates transcription

The mRNA is translated into proteins .

Regulaation of gene expression by steriod hormones

The hormones interacts with a receptor inside its target cells & resulting complex moves into the

nucleus , where it activate the transcription of particular gene

Regulation of gene by steroid hormone

Regulation of gene expression at Translational

level.

1. Translation Control

Blocking mRNA Attachment to

Ribosomes

2. Regulation of Protein Processing

Protein Modification

Inititation factors are subjected to phosphorylation by a no. of protein kinases.

Some protein binds directly to mRNA & Act as translational repressor, many of them binding at specific sites in the 3’ un translated region .

initiation of transcription

1

mRNA splicing

2

mRNA protection3

initiation of translation

6

mRNAprocessing

5

1 & 2. transcription - DNA packing - transcription factors

3 & 4. post-transcription - mRNA processing

- splicing- 5’ cap & poly-A tail- breakdown by siRNA

5. translation - block start of translation

6 & 7. post-translation - protein processing - protein degradation

7 protein processing & degradation

4

4

Gene Regulation

Discussion Regulation of Gene Expreesion in Eukaryotes

:Any of the processes by which nuclear, cytoplasmic, or intercellular factors influence the differential control of gene action during the developmental stages of an organism. 

THANK YOU