Mr. Prabhat Kumar Singh presented on transcriptional and post-transcriptional regulation of gene expression. There are two main steps in gene expression - transcription and translation. Transcription involves creating mRNA with RNA polymerase enzymes. Translation involves using mRNA to direct protein synthesis. Regulation can occur at multiple levels including replication, transcription, post-transcription, and translation. Transcriptional regulation differs between prokaryotes and eukaryotes due to eukaryotes having nuclei. Prokaryotes use operon systems like the lac and trp operons to regulate transcription. Eukaryotes use promoter elements like TATA boxes. Post-transcriptional regulation in eukaryotes includes RNA splicing and modifications. Pro

1. Assignment Presentation
On
Transcriptional and Post-transcriptional Regulation of
Gene Expression
Presented By
Mr. Prabhat Kumar Singh
Ph. D. Agril. Biotechnology
Course Title: Plant Molecular Biology
(MBB-601)

2. Gene Expression
 It is a process in which the genetic codes of genes are used to control protein
synthesis, which is necessary for our bodies to form cell structures.
 Structural genes are genes that carry information that is needed for amino acid
sequencing.
There are two main steps in this procedure:
1. Transcription– The messenger RNA is created in this stage with the help of RNA
polymerase enzymes, resulting in the processing of mRNA molecules.
2. Translation– The primary purpose of mRNA is to direct protein synthesis, which
leads to post-translational processing of the protein molecules.

3. Regulation of Gene Expression at Various Levels:
Fig: Gene Regulation

4. Regulation of Gene Expression
 Stimulates the expression of certain genes and inhibits that of others is called
regulation of gene expression. In eukaryotes, the regulation could be exerted at,
as explained below.
1. Replication level – Gene expression may be affected by mutations that occur
during DNA replication.
2. Transcriptional level – The Repressors and activators can influence the
transcription of a specific gene.
3. Post-transcriptional level – Post-transcriptional changes, such as RNA splicing, can
result in gene expression.
4. Translational level – RNA interference mechanism, for example, can influence the
translation of an mRNA molecule.

5. Regulation of Gene Expression in Prokaryotes and Eukaryotes:
 Regulation of genes differs depending on whether the organism is prokaryotic or
eukaryotic.
 Eukaryotes are multicellular and unicellular organisms with nuclei and other
organelles within their cells, such as mammals, fungi, plants, and protists.
 Prokaryotes are single-celled organisms without a nucleus, such as bacteria.
Because eukaryotes have a nucleus and prokaryotes do not, prokaryotic and
eukaryotic transcription regulation is fundamentally different.
Fig: Regulation of Gene Expression in Prokaryotes and Eukaryotes

6.  The variation in the rate of transcription often regulates gene expression.
Interactions between RNA polymerase II and basal transcription factors leading to
the formation of the transcription initiation complex influence the rate of
transcription.
 Other transcription factors change the rate of transcription initiation by binding to
promoter sequences.
 The rate of transcription is also influenced by enhancers and silencers.
Transcriptional Regulation of Gene Expression in Eukaryotes:

7.  Promoter:
 This is a site for regulation of transcription. Every structural gene in eukaryotes has
the promoter site which consists of several hundred nucleotide sequences that
serve as the recognition point for RNA polymerase binding, located at a fixed
distance from the site where transcription is initiated.
 Eukaryotic promoters require the binding of a number of protein factors to initiate
transcription.
 Promoter regions are recognized by RNA polymerase II, which transcribes
primarily mRNA, consists of short DNA sequences usually located within 100 bp
upstream (in the 5′ direction) of the gene.

8. The promoter regions of most eukaryotic gene contain several
specific regions such as:
a. TATA box
b. CAAT box
c. GC box
 TATA Box:
 Variation in the rate of transcription often regulates gene expression.
 Interactions between RNA polymerase II and basal transcription factors lead to
formation of transcription initiation complex (TIC) at the TATA box.
 It is located about 25-30 bases upstream from the initial point of transcription, it
consists of an 8 bp consensus sequence composed of A = T base pairs (TATAAA)
only, but flanked on either side by G=C rich regions.
 Mutation in TATA box reduces transcription or may alter the initiation point. TATA
box is also known as Hogness box.

9.  CAAT Box:
 Many promoters contain other components and also bear the consensus
sequence like GGCCAATC which is situated at the region 70-80 bp from the start
site, it can function in both 5-3′ or a 3-5′ orientation.
 Mutational analysis showed that CAAT box plays the strongest role in
determining the efficiency of the promoter.
 GC Box:
 Another element often seen in some promoter regions, called the GC box, has
the consensus sequence GGGCGG and is found at about position -110, often
occurs in multiple copies, the GC elements bind transcription factors and
function more like enhancer.

10. Post-Transcriptional Regulation of Gene Expression in
Eukaryotes:
Post-transcriptional regulation of gene expression may occur in different ways.
 Post-transcriptional modes of regulation also occur in many organisms where the
eukaryotic nuclear RNA transcripts are modified prior to translation, non-coding
introns are removed, the remaining exons are precisely spliced together and the
mRNA is modified by the addition of cap at the 5′ end and a poly-A tail after end.
Regulation at translational level occurs in different ways:
(i) Activation and repression of translation:
 In eukaryotes the activator protein binds to mRNA and leads to the formation of
hairpin structure which helps in ribosome binding with mRNA by the exposure of
5′ end.
 The translational repressor protein (IRE-BP) controls ferritin synthesis by down-
regulation and transferring receptor synthesis by up-regulation.

11. (ii) Regulation by phosphorylation machinery:
 Translational repressor protein may regulate the translation in eukaryotic system
or regulation of translation is brought about by modification of general
components of translational machinery.
 Reversible phosphorylation machinery is involved in the regulation of gene
expression, as the phosphorylated or dephosphorylated forms of the
components of translational machinery should identify a specific mRNA from the
bulk mRNA population.

12. Transcriptional Regulation of Gene Expression in Prokaryotes:
 Gene transcription is regulated in bacteria through a complex of genes termed
operon. These are transcriptional units in which several genes, with related
functions, are regulated together.
 Other genes also occur in operons which encode regulatory proteins that control
gene expression. Operons are classified as inducible or repressible.
 Inducible and Repressible System:
 The β galactosidase in E. coli is responsible for hydrolysis of lactose into glucose
and galactose.
 If lactose is not supplied to E. coli cells, the presence of β galactosidase is hardly
detectable. But as soon as lactose is added, the production of β galactosidase
enzyme increases. The enzyme falls as quickly as the substrate (lactose) is
removed.

13. Operon Model:
 An operon is a cluster of bacterial genes along with an adjacent promoter that
controls the transcription of those genes.
 They usually control an important biochemical process.
 They are only found in prokaryotes. -
first proposed the operon model of gene regulation For their significant
contribution in field of biochemistry, they were awarded
.
 The first system of gene regulation that was understood was the lac operon in E.
coli.
Fig: Structure of Operon

14. Classify genes in simple way in two classes:
1. Structural Gene: Any non-regulatory gene that codes for the production of a
specific RNA, structural protein, or enzyme.
2. Regulatory Gene: The genes that code for regulator factors are known as
regulatory genes. The expression of one or more genes is controlled by these
regulatory factors.
Two examples of how these molecules regulate separate operons are shown below.
1. The Trp Operon: A Repressor Operon
 Bacteria, like all cells, require amino acids to survive. E. coli may either swallow
or generate tryptophan, an amino acid that it can obtain from the environment.
 E. coli must express a set of five proteins encoded by five genes when it wants to
produce tryptophan.
 In the tryptophan (trp) operon, these five genes are positioned adjacent to each
other.

15. 2. The lac Operon: An Inducer Operon
 Represented by the letter ‘Lac’ in Lac Operon. Lac Operon is an example of
transcription control.
 In many intestinal bacteria, including E. coli, it regulates the transcription of
genes that code for enzymes involved in the transport and metabolism of
lactose.
There are two types of genes in Lac Operon: structural genes and regulatory genes.
 Lac Z, LacY, and Lac A are structural genes in Lac Operon that code for enzymes
involved in lactose transport and metabolism.
1. lac Z: It codes for the enzyme -galactosidase, which hydrolyzes lactose to produce
glucose and galactose, as well as converting lactose to its isomeric form, allolactose.
2. lac Y: It codes for the -galactoside permease enzyme, which is a transporter
protein that helps lactose enter the cell.
3. lac A: The enzyme -galactoside transacetylase is encoded by this gene. This
enzyme eliminates toxic -galactosides, glucosides, and lactosides from the cell by
transferring an acetyl group from acetyl-CoA.

16. Post-Transcriptional Regulation of Gene Expression in
Prokaryotes:
Gene regulation may also occur in prokaryotes at the time of translation.
 Autogenous Regulation of Translation:
 There are number of examples where a protein or RNA regulates its own
production. Several proteins work as repressors, bind to the ribosome binding
site (or SD-Shine-Dalgarno sequence) or initiation codon of mRNA.
 In these cases mRNA remains intact but cannot be translated.
 There are some other systems where mRNA may be degraded by the binding of
protein on the short specific sequences of mRNA.
 Regulation by Anti-sense RNA:
 Translational control of protein synthesis can be exercised by using RNA which is
complementary to mRNA, these complementary RNA will form RNA- mRNA
hybrids and prevent mRNA from being translated.
 These kind of RNAs are called anti- sense RNA or micRNA (mic = mRNA
interfering complementary RNA).

17.  Repression of Translation:
Repression of translation occurs by the following ways:
(a) A repressor-effector molecule may recognise and bind to a specific sequence or
to a specific secondary structure (involving SD region and AUG codon), thus blocking
initiation of translation through blocking of the ribosomal binding region.
(b) A repressor-effector molecule may bind to an operator (not involving SD region
and AUG codon) thus stabilizing an inhibitory mRNA secondary structure.
(c) An effector molecule (an endonuclease) can inhibit initiation of translation by
endonucleolytic cleavage of SD region.
References:
1. Kuhlemeier, C. (1992). Transcriptional and post-transcriptional regulation of gene
expression in plants. Pl. Mole. Biol., 19: 1-14.
2. Ghedira, K. (2018). Introductory Chapter: A Brief Overview of Transcriptional and
Post-transcriptional Regulation. intechopen.79753.