Transcript THE REGULATION OF TRANSCRIPTION

Transcription
Nicky Mulder
Acknowledgements: Anna Kramvis for lecture
material (adapted here)
Central dogma of molecular biology
http://www.cem.msu.edu/~reusch/VirtualText/nucacids.htm
Copyright-Anna Kramvis
2
DNA -> RNA -> PROTEIN
GENES are
transcribed/expressed
Converts information
from DNA into a usable
template for protein
What is a gene?
 Segment
of DNA that is transcribed
into RNA
 This RNA can be:
–rRNA, tRNA, siRNA,
antisense RNA
Protein coding –messenger RNA
(mRNA)
Non-coding
Copyright-Anna Kramvis
4
Parts of genes
The part of a coding gene that is
translated into a protein is the Open
Reading Frame (ORF)
 Within the ORF, triplets of bases (codons)
code for amino acids via the genetic code
 An ORF starts with an initiation codon and
ends with a stop codon

Copyright-Anna Kramvis
5
Prokaryotic genes
Promoter region
-35
Open reading frame
-10
Initiation site
Regulatory regions
Ribosome
binding site
Termination site
Prokaryotic genes cont.
Can be encoded on different strands: forward or reverse
Some are in operons
Promoter
One transcript
Eukaryotic genes
Many eukaryotic genes include introns and
exons
 Coding part is in the exons which need to
be joined

open reading frame
5’
upstream
exon
initiation codon
intron
exon downstream
termination codon
3’
Eukaryotic gene reality
Small exons, large introns!
Exons are joined by splicing –
can lead to multiple products
Alternative splicing
Splice junction
Exon 1
Exon 2
Intron 1
Exon 2
Exon 1
Exon 2
Exon 3
Exon 1
Intron 2
Exon 3
Exon 3
Exon 2
Exon 3
Transcription and translation steps
Prokaryotes
Eukaryotes
Why the RNA step?
MASTER COPY
FLEXIBLE &
DISPENSABLE
Transcription
FINDING PROMOTER
INITIATION
ELONGATION
Transcription initiation
RNA Polymerase enzymes
Prokaryotes:
1 RNA polymerase, 4 subunits , , ’, 
Eukaryotes:
3 different RNA polymerases, I, II, III each 12-16 subunits
II is most well studied
Prokaryotic RNA Polymerase
SIGMA FACTOR IS
IMPORTANT FOR
PROMOTER FINDING
AND BINDING BY
RNA POLYMERASE
Eukaryotic RNA Polymerase II
Transcription
initiation from RNA
Polymerase II
Regulation of transcription -activation
ADDITIONAL
TRANSCRIPTION
FACTORS
 /TF
ENHANCER
ENHANCER
PROTEIN
RNA
POLYMERASE
PROMOTER
CO-ACTIVATOR
Regulation of transcription -repression
ANTI- FACTOR
 /TF
ENHANCER
RBS
RNA
POLYMERASE
REPRESSOR
REPRESSOR
REPRESSOR
PROMOTER
-HISTONE DEACETYLATION
-DNA METHYLATION
-CHROMATIN STRUCTURE
-AUTOREGULATION
Sigma factors
Transcription factors have DNA binding
region and protein interaction domain
Sigma factor
structure
-10
-35
NH2
COOH
CORE BINDING REGION
MAJOR  FACTORS HOUSEKEEPING GENES

RNA
POLYMERASE
ALTERNATIVE 
FACTORS
RNA
POLYMERASE
STRESS RESPONSE

OTHER FUNCTIONS
EXTRACYTOPLASMIC


Regulation of  factors
Autoregulation of its own expression
 Regulation of expression by external
signals
 Half-life of RNA or protein
 Relative abundance of different  factors
 Regulation by anti-sigma factors
 Proximity of the sigma factors

Regulation by sigma factors
SPORULATION IN BACILLUS
HEAT SHOCK RESPONSE
Transcription and drug targets
RNA polymerase  subunit is target for
anti-TB drug rifampicin
 SigB regulates katG- involved in INH
resistance
 Other transcription factors that have a
core role in the control of expression of
specific sets of genes eg IdeR

Gene regulation in humans
Multicellular organisms need intra-cellular signals controlled by gene
expression. Up to 10% of human genes may encode TFs.
NF-KB
TP1
AP-1
STAT
Transcription regulation and
human disease
Heart failure - Switch between 2
different metabolic pathways
 Huntington’s disease - polyglutamine
stretches & transcription dysregulation
 Cancer - oncogenes and antioncogenes overexpression of genes,
P53

Gene expression is NB
Having the right proteins at the right time
 No waste in producing what you don’t
need
 Being able to respond quickly to changes
 Getting the right regulators present to
control gene expression

Additional features of RNAs
Have ability to fold into secondary
structures
 RNAs can be catalytic –ribozymes
 RNAs can regulate transcription or
translation
 RNAs can be genomes

Antisense RNAs
Complementary to a piece of mRNA
 Bind and prevent translation
 Important form of post-transcriptional
regulation
