transcription nicky mulder acknowledgements: anna kramvis for lecture material (adapted here)
TRANSCRIPT
Transcription
Nicky Mulder
Acknowledgements: Anna Kramvis for lecture material (adapted here)
Copyright-Anna Kramvis 2
Central dogma of molecular biology
http://www.cem.msu.edu/~reusch/VirtualText/nucacids.htmhttp://www.cem.msu.edu/~reusch/VirtualText/nucacids.htm
DNA -> RNA -> PROTEIN
GENES are transcribed/expressed
Converts information from DNA into a usable template for protein
Copyright-Anna Kramvis 4
What is a gene?
Segment of DNA that is transcribed into RNA
This RNA can be:Non-coding –rRNA, tRNA, siRNA,
antisense RNAProtein coding –messenger RNA
(mRNA)
Copyright-Anna Kramvis 5
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
Prokaryotic genes
Promoter region
-35 -10
Regulatory regions
Open reading frame
Initiation site
Ribosome binding site
Termination site
Prokaryotic genes cont.
Can be encoded on different strands: forward or reverse
Promoter
Some are in operons
One transcript
Eukaryotic genes Many eukaryotic genes include introns and
exons Coding part is in the exons which need to
be joined
3’3’
exonexon exonexonintronintron
open reading frameopen reading frame
upstreamupstream downstreamdownstream5’5’
initiation codoninitiation codon termination codontermination codon
Eukaryotic gene reality
Small exons, large introns!
Exons are joined by splicing –can lead to multiple products
Alternative splicing
Exon 1 Intron 1 Exon 3Exon 2 Intron 2
Exon 1 Exon 2 Exon 3
Exon 3
Exon 3
Exon 1Exon 2
Exon 2
Splice junction
Transcription and translation steps
ProkaryotesEukaryotes
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
PROMOTER
RNA POLYMERASE
/TF
ENHANCER
CO-ACTIVATOR
ADDITIONAL TRANSCRIPTION
FACTORS
ENHANCER PROTEIN
Regulation of transcription -repression
PROMOTERRNA
POLYMERASE
/TF
ENHANCER
ANTI- FACTOR
REPRESSOR
REPRESSOR
REPRESSOR
RBS
-HISTONE DEACETYLATION
-DNA METHYLATION
-CHROMATIN STRUCTURE
-AUTOREGULATION
Sigma factors
NH2 COOHCORE BINDING REGION
-10 -35
Transcription factors have DNA binding region and protein interaction domain
Sigma factor structure
RNA POLYMERASE
MAJOR FACTORS -HOUSEKEEPING GENES
RNA POLYMERASE
STRESS RESPONSE
EXTRACYTOPLASMIC
OTHER FUNCTIONS
ALTERNATIVE FACTORS
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 factorsSPORULATION 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
NF-KB
TP1
AP-1
STAT
Multicellular organisms need intra-cellular signals controlled by gene expression. Up to 10% of human genes may encode TFs.
Transcription regulation and human disease
Heart failure - Switch between 2 different metabolic pathways
Huntington’s disease - polyglutamine stretches & transcription dysregulation
Cancer - oncogenes and anti-oncogenes 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