Lecture Notes on Regulation of Gene Expression (MCB2020F)

Regulation of Bacterial Gene
Expression
REGULATION OF BACTERIAL GENE EXPRESSION............................................................................................. 1
BACKGROUND..........................................................................................................................................................2
LEVELS OF REGULATION OF GENE EXPRESSION...............................................................................................................2
In Bacteria:......................................................................................................................................................2
In Eukarya:......................................................................................................................................................2
2 Levels of regulation:.....................................................................................................................................3
KEY TERMS..............................................................................................................................................................3
POSITIVE & NEGATIVE CONTROL.................................................................................................................................4
Positive Control...............................................................................................................................................4
Negative Control.............................................................................................................................................5
REGULATION AT TRANSCRIPTIONAL INITIATION..............................................................................................................5
POST-TRANSCRIPTIONAL REGULATION..........................................................................................................................5
TRANSLATIONAL REGULATION.....................................................................................................................................5
REGULATION OF TRANSLATION BY A RIBOSWITCH..........................................................................................................6
THE LAC OPERON.....................................................................................................................................................6
Catabolite Activator Protein (CAP)..................................................................................................................8




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, Regulation of Bacterial Gene
Expression
Background
- Very few cell proteins are produced continuously
- Number of mRNA transcripts and amount of proteins are regulated
- The expression of individual or groups of genes need to be modulated
- Amount of protein varies according to changing environmental & metabolic need:
o Availability of a substrate (e.g. carbohydrate)
 Enzymes are produced to use the substrate
o Excess of end product of metabolic pathway
 Enzymes used to make that product are repressed; i.e. pathway is
closed
o Stress responses (e.g. heat, starvation, DNA damage)
 Enzymes produced to support cell survival


Levels of regulation of Gene Expression

In Bacteria:
Transcription:
- Genetic regulatory proteins can bind to DNA and control whether or not
transcription begins [Same in Archaea]
- Attenuation: transcription can terminate very early due to formation of a
transcriptional terminator
o Binding of a metabolite to a riboswitch in mRNA can cause premature
termination

Translation:
- Translational repressor proteins can bind to mRNA and prevent translation from
starting
- Antisense RNA can bind to mRNA and control whether translation begins
- Binding of metabolite to a riboswitch can block translation [Same in Archaea]

Post translation: [Same in Archaea]
- Small mols can bond non-covalently to a protein and affect its function
o E.g. feedback inhibition
- Structure and function of a protein can be altered by covalent changes in protein
o Can be reversible or irreversible

In Eukarya:
Transcription:
- Regulatory transcription factors may activate or inhibit transcription
- Compaction level of chromatin influences transcription
- DNA methylation usually inhibits transcription



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