cis-regulatory element study in transcriptome jin chen cse891-001 fall 2012 1
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cis-regulatory element study in transcriptome
Jin ChenCSE891-001
Fall 2012
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What is Cis-element
Courey and Jia (2001)
A cis-regulatory element or cis-element is a region of DNA or RNA that regulates the expression of genes located on that same molecule of DNA
Latin word “cis” means "on the same side as"
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Cis-element properties• Typically found in 5’ untranscribed region of the
gene (promoter region)
• Can be specific sites for binding of activators or repressors
• Position and orientation of cis-element relative to transcriptional start site is usually fixed
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Cis-element properties
• Short sequences• Recurring patterns • Sequence-specific binding sites
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Cis-element Representations
A G T A T AA G A T T AC G A C T CA G T G T AA G T G T G
Consensus sequence:
Prob(A) 0.8 0 0.4 0.2 0 0.6
Prob(C) 0.2 0 0 0.2 0 0.2
Prob(G) 0 1 0 0.4 0 0.2
Prob(T) 0 0 0.6 0.2 1 0
ProbabilityMatrix & sequence logo:
A G W N T A
Sequence 1:Sequence 2:Sequence 3:Sequence 4:Sequence 5:
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Cis-element Representation 1
• Consensus based method– Refer to a sequence that
matches all examples of the binding site closely but not exactly
– Trade-off between ambiguity and sensitivity
code descriptionA AdenineC CytosineG GuanineT ThymineU UracilR Purine (A or G)Y Pyrimidine (C, T, or U)M C or AK T, U, or GW T, U, or AS C or GB C, T, U, or G (not A)D A, T, U, or G (not C)H A, T, U, or C (not G)
V A, C, or G (not T, not U)
N Any base (A, C, G, T, or U)
IUPAC codes
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Cis-element Representation 2
• Sequence logos
– A visual representation of the probability matrix
– The total height of each column is proportional to its information content
http://www-lmmb.ncifcrf.gov/~toms/sequencelogo.html
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Cis-element matching/discovery
• Pattern Matching– Discovery patterns in sequences from co-regulated
genes using JASPAR and TRANSFAC matrices– Pscan
• Pattern Discovery– Discovery patterns in sequences from co-regulated
genes without using known patterns – MEME, hmmbuild
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Pattern Matching
http://www.slideshare.net/Stewbacca/dna-motif-finding-2010
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Pattern Matching
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Pattern Matching
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http://159.149.109.9/pscan/
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Cis-element evolution
• Composition• Location• Modules
chiken aA
mouse aA
mouse d1
Gene control regions for eye lens chrystallins
Molecular Biology of the Cell, Alberts et al., 4th ed.
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Large Scale Analysis
• Identify 264 co-regulated gene groups in S. serevisiae• Putative cis-regulatory elements– 80 known consensus binding sites– 597 elements by motif discovery with MEME
• Score enrichment of genes containing each putative element- 42 cis-elements in 35 unique groups
• Orthologous modules in other species• Enrichment of orthologous modules
A. P. Gasch et al., PLoS Biol., 2004
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Conservation of S. cerevisiae motifsG1 phase cell cycle ACGCG MCBAmino acid biosynthesis TGACTM Gcn4pNitrogen source GATAA GATA factors
Proteasome GGTGGCAAA Rpn4p
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Positions of binding sites
• Non random distribution• Similar across species• No correlations in locations
across species
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Spacing between binding sitesin Methionine Biosynthesis genes
• Small distance between Cbf1p and Met31/32p• Conserved across species• Independent of exact positions
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Control of iron metabolism in Mycobacterium tuberculosis. Rodriguez, Marcela. Trends in Microbiology, 2006.
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Poisson Method for module discovery
Look for matches to consensus sequences
Mcm1 : DCCYWWWNNRG
Ste12 : TGAAACA
Random DNA sequence:
“Pearson type III distribution”:
2
( 2)!k axa
pdf x ax ek
Exponential distribution:
axpdf x ae
Wagner A (1999) Bioinformatics 15(10): 776-784
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Cister & Comet
DNA sequence segment
Prob segment | cluster modelscore segment ln
Prob segment | random model
Cluster model:
Poisson-distributed cis-elements, embedded in random DNA
Frith MC, Hansen U, Weng Z (2001) Bioinformatics 17(10): 878-889. Frith MC, Spouge JL, Hansen U, Weng Z (2002) Nucleic Acids Research