Eukaryotic Transcription gene regulation

Dr.V.Malathi

Main Body

Eukaryotic Transcription gene regulation

Dr.V.Malathi

Transcriptional Regulation in Eukaryotes

There are three classes of control elements in eukaryotes:

•The RNA polymerase II binding region (the core promoter)

• cis-acting binding sequences that bind to proteins with RNA polymerase affinity, which in turn help bind RNA polymerase to a promoter.

•A trans-acting DNA element

cis-acting DNA element

•These are short DNA sequences that acts as a binding site for a protein that has an affinity for that specific sequence.

include short consensus sequences

• These elements are usually located within 200 bp upstream of the transcription initiation site

•They can be included in a promoter or an enhancer

• They have an affinity for a specific protein that binds to it, serving as a regulator

•The term “cis acting” means that the bound protein acts only upon DNA sequences on the same DNA molecule as the cis-acting sequence.

•These are also found in prokaryotes example ; the operator of the lac operon.

cis-acting DNA elements- enhancers and silencers

•An enhancer DNA sequence (or positive regulatory element) turns a gene ON.

•When the activator is bound to the enhancer, RNA polymerase is more highly attracted to the gene.

•enhancers are located upstream or downstream of the promoter region,

•Multiple regulatory proteins bound to binding sites in an enhancer can form a large, complex enhancesosome that has varying affinity for RNA polymerase, depending on its size and exact composition.

•The enhanceosome can both recruit additional co-activators and facilitate chromatin remodeling.

•A silencer DNA sequence (or negative regulatory element) turns a gene OFF or reduces its rate of transcription.

•When the repressor is bound to the silencer, RNA polymerase cannot attach and transcribe the gene.

•silencers are located downstream of a promoter.

Trans-acting DNA element

•A trans-acting DNA element is a DNA sequence that codes for a protein (a trans-acting factor) that controls the expression of a gene at a separate location by binding to its cis-acting element.

Trans-acting factors:

• These are enzymes that interact with RNA polymerase

• They bind to RNA polymerase to stabilize the initiation complex

• They may bind to a few promoters and serve as positive regulators

•A trans-acting factor can affect the expression of genes located on separate chromosomes.

Post-Translational Control of Gene Expression

RNA is transcribed, but must be processed into a mature form before translation can begin. This processing is called post-transcriptional modification.
This post-transcriptional step can also be regulated to control gene expression in the cell.
In eukaryotic RNA transcript often contains regions, called introns, that are removed prior to translation.
The regions of RNA that code for protein are called exons .
By a process called , the RNA is processed and the introns are removed and exons are ligated together.

Picture depicting RNA splicing

“Pre-mRNA can be alternatively spliced to create different proteins” by Shelli Carter and Lumen Learning. is licensed under CC BY 4.0

ALTERNATIVE RNA SPLICING

Alternative RNA splicing is a mechanism that allows different protein products to be produced from one gene when different combinations of introns, and sometimes exons, are removed from the transcript.
Alternative splicing acts as a mechanism of gene regulation,
The frequency of different splicing alternatives controlled by the cell as a way to control the production of different protein products in different cells or at different stages of development.
70 percent of genes in humans are expressed as multiple proteins through alternative splicing.

Splicing Overview

“Splicing_overview.jpg” by Agathman is licensed under CC BY-SA 3.0

Control of RNA Stability

The 3′ and 5′ ends of the mRNA is protected before it leaves the nucleus,
.The 5′ end of the mRNA is protected by a 5′ cap, which is usually composed of a methylated guanosine triphosphate molecule (GTP).
The poly-A tail protects the 3′ end. It is usually composed of a series of adenine nucleotides.
The length of time that the RNA resides in the cytoplasm can be controlled.
Each RNA molecule has a defined lifespan and decays at a specific rate. This rate of decay determine how much protein is in the cell. For example , If the decay rate is increased, the RNA will not exist in the cytoplasm as long, shortening the time for translation to occur.
This rate of decay is referred to as the RNA stability
Proteins, called RNA-binding proteins, or RBPs, can bind to the regions of the RNA just upstream or downstream of the protein-coding region. These regions in the RNA that are not translated into protein are called the
These regions regulate mRNA localization, stability, and protein translation. The region just before the protein-coding region is called the 5′ UTR, whereas the region after the coding region is called the 3′ UTR .
The binding of RBPs to these regions can increase or decrease the stability of an RNA molecule, depending on the specific RBP that binds.

5′ and 3′ untranslated regions (UTRs). The presence of RNA-binding proteins at the 5′ or 3′ UTR influences the stability of the RNA molecule.

“The protein-coding region of mRNA is flanked by 5′ and 3′ untranslated regions (UTRs). The presence of RNA-binding proteins at the 5′ or 3′ UTR influences the stability of the RNA molecule.” by Shelli Carter and Lumen Learning is licensed under CC BY 3.0

microRNAs

microRNAs, or miRNAs, are short RNA molecules that are only 21–24 nucleotides in length.
The miRNAs are made in the nucleus as longer pre-miRNAs.
A protein called dicer chop these pre-miRNAs are chopped into mature miRNAs .
Mature miRNAs recognize a specific sequence and bind to the RNA and associate with a ribonucleoprotein complex called the RNA-induced silencing complex (RISC).
RISC binds along with the miRNA to degrade the target mRNA. Together, miRNAs and the RISC complex rapidly destroy the RNA molecule.

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Eukaryotic Transcription gene regulation by Dr.V.Malathi is licensed under a Creative Commons Attribution-ShareAlike 4.0 International License, except where otherwise noted.