Gene expression in prokaryotes like E. coli can be regulated at the level of enzymes or transcription. Enzyme regulation includes induction, repression, and feedback inhibition which control enzyme synthesis or activity. Transcription regulation includes negative regulation by repressors, positive regulation by activators, auto-regulation of a gene by its own protein product, and coordinate regulation of multiple enzymes from a single mRNA molecule.

2. INTRODUCTION
• Gene expression refers to the manifestation of
a phenotypic character by the activity of gene.
• A gene expresses its character by producing a
protiens or enzymes.
• During gene expression,there is flow of
genetic information from DNA to protiens.
• Gene expression involves two main steps
namely, TRANSCRIPTION and TRANSLATION.

4. REGULATION OF GENE
EXPRESSION IN PROKARYOTES
• Regulation of gene expression is well studied
in the bacterium Escherichia coli.
• Normally gene expression is regulated at 2
levels.they are:
• Regulation of enzyme
• Regulation of transcription

5. REGULATION OF ENZYME
• In E.coli,certain enzymes are continously produced
,regardless of their needs .these enzymes are called
CONSTITUTIVE ENZYMES. They require no gene regulation.
• Certain other enzymes are synthesized only when they are
needed.such enzymes are called REGULATED
ENZYMES.they require gene regulation.
• The following regulation of enzymes mechanisms are:
ENZYME INDUCTION.
ENZYME REPRESSION.
FEEDBACK INHIBITION.

6. ENZYME INDUCTION
• When substract is present in the medium,an
enzyme is synthesized by the bacterium to
metabolise the substrate.this phenomenon is
called ENZYME INDUCTION.
• The substract which is responsible for the
production of the enzyme is called INDUCER
and the enzyme is called INDUCIBLE ENZYME.

7. ENZYME REPRESSION
• Certain enzymes are normally synthesized and
are present at all time in the cell.
When the end product is produced in large
amount, the enzyme synthesis is stopped.this
phenomenon is called ENZYME REPRESSION.

8. FEEDBACK INHIBITION
• In feedback inhibition,the enzyme activity is
inhibited by the end product when it is
produced in excess.hence it is also called END
PRODUCT INHIBITION.
• “HERE THE ENZYME SYNTHESIS IS NOT
INHIBITED ;BUT THE ENZYME ACTIVITY IS
INHIBITED”.

9. REGULATION OF TRANSCRIPTION
• Transcription refers to the synthesis of mRNA
from DNA. it is a stage in gene expression.
• In prokaryotes,the genes are regulated at the
level transcription.
• There are 4 types of regulation of
transcription.they are:
• Negative regulation
• Positive regulation
• Auto regulation
• Co-ordinate regulation

10. NEGATIVE REGULATION
• Blocked gene is set free for transcription.
• Inhibitor present in the cell,prevents transcription.
• The inhibitor is a regulator protein called REPRESSOR.
• The transcription is initiated by another protein called
INDUCER.
• The inducer binds with the inhibitor and makes the
gene free to initiate transcription.
• In a biosynthetic pathway,absence of the end product
usually increases its synthesis and presence of the
product decreases its synthesis.

11. POSITIVE REGULATION
• Inducer activates a gene .the activator
molecule attaches to the initiator site on the
gene and the transcription is initiated.
• The positive regulation may be of the
inducible or repressible type.
• In the inducible system,the effector molecule
functions as the inducer.
• In the repressible system,the effector
molecule is the corepressor.

12. AUTO REGULATION
• The protein synthesized by a gene,directly
inhibits the transcription by the same
gene,when the protein is produced in high
concentration.
• This protein is translated from a monocistronic
mRNA.

13. COORDINATE REGULATION
• When several enzymes acts the regulation is
brought about the none of the enzymes.
• Inhibition of synthesis of all enzymes,it results
from the control of the synthesis of a single
polycistronic mRNA molecule encoding all of
the enzymes.
• It doesnot occur in eukaryotes because
eukaryotic mRNA is usually monocistronic.