Maribyrnong College Biology Unit 4
Promoter Sequence – Revision
Promoter is a region of DNA ‘upstream’ of a gene (i.e. towards the 5’ end of the sense
strand) that facilitates the binding of the RNA polymerase (RNA polymerase II in
eukaryotes) enzyme.
Promoter sequence is recognised by RNA polymerase and (in prokaryotes) a sigma ()
factor (this is brought to the DNA by an activator protein) that also binds to the DNA
further upstream. In eukaryotes, there are at least seven different factors necessary for
the binding of RNA polymerase II.
Promoter elements
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Core promoter – minimal portion of promoter
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Transcription Start Site (TSS) (DNA code TAC)
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Approximately 34 base pairs upstream
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A binding site for RNA polymerase
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General transcription factor binding sites
Proximal promoter – proximal sequence upstream that contains primary regulatory
elements
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Approximately 250 base pairs upstream
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Specific transcription factor binding sites
Distal promoter – distal sequence further upstream that may contain additional
regulatory factors
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Weaker influence on transcription than proximal promoter
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No set distance upstream
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Specific transcription factor binding sites
Prokaryotes
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Promoter consists of two short sequences upstream of the gene being transcribed at
-10 and -35 base pairs upstream from Transcription Start Site (TSS).
-10 site is called the Pribnow box (also known as the Pribnow-Schaller box, named
after David Pribnow and Heinz Schaller who first sequenced the region of DNA
in 1975).
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Usually consists of the six nucleotides TATAAT.
It is essential for transcription
-35 site (-35 element) usually consists of the six nucleotides TTGACA
Eukaryotes
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Promoter sequences very diverse and unable to be characterised.
Lie upstream of gene.
May have regulatory elements 1,000s of base pairs away (called enhancers).
Can cause DNA strand to bend back on itself.
Many eukaryote promoters contain a TATA box (TATAAA) which binds a TATA
binding protein which assists the formation of the RNA polymerase transcriptional
complex
TATA box usually -50 base pairs upstream of TSS.
Eukaryote promoter regulatory sequences usually bind proteins called Transcriptional
Factors (which are involved in the formation of the transcription complex).
See Nature of Biology page 375 ‘Coding and Flanking Regions’
Maribyrnong College Biology Unit 4
Regulation of Genes
Example: Lac operon in E.coli
Lactose broken down into galactose and glucose
Two proteins required Beta galactosidase and Beta galactoside permesase
Lac Operon animation
http://www.sumanasinc.com/webcontent/animations/content/lacoperon.html
http://www.biostudio.com/d_%20Lac%20Operon.htm
RNA Transcription animation
http://spine.rutgers.edu/cellbio/assets/flash/transcript.htm
Gene Expression animation
http://www.genomicseducation.ca/animations/gene_expression.asp
Transcription
http://www.biologycorner.com/bio4/notes/gene-expression.php
http://www.stolaf.edu/people/giannini/flashanimat/molgenetics/transcription.swf
http://pages.csam.montclair.edu/~smalley/transcription.mov