nucleosome positioning & transcription factor identification
DESCRIPTION
Nucleosome Positioning & Transcription Factor Identification. Zhang Zhizhuo May 2010. Outline. Basic Concept Nucleosome Positioning and Gene Regulation General Transcription Mechanism Genomic Organization of Nucleosomes The Organization of Nucleosomes on Genes Control of DNA Access - PowerPoint PPT PresentationTRANSCRIPT
ZHANG ZHIZHUOMAY 2010
Nucleosome Positioning& Transcription Factor Identification
Outline
Basic ConceptNucleosome Positioning and Gene Regulation
General Transcription Mechanism Genomic Organization of Nucleosomes The Organization of Nucleosomes on Genes Control of DNA Access
Nucleosome Related TF Identification Enhancer Identification Integrating Histone Information to Predict TF binding
sites
Basic Concept
Histone
Nucleosome
Basic Concept
HistoneNucleosomeLinker-DNA
DNA between two nucleosomesRNA PolyII
An enzyme catalyzes the transcription of DNATBP
TATA binding protein and a necessary component of RNA polymerase
General Transcription Mechanism
”Bridge”
Chromatinremodelling
General Transcription Mechanism
Genomic Organization of Nucleosomes
Deposition of histones on DNA during DNA replication occurs at random positions?
Not Really!
Genomic Organization of Nucleosomes
Highly phased or a random continuous distribution
Genomic Organization of Nucleosomes
Highly phased or a random continuous distribution
Facing inwards or outwards
Distance between Positioned nucleosomes
Tend to be fixed distanceshort stretches of linker DNA
165 bp (18 bp linker) in S. cerevisiae 175 bp (28 bp linker) in D. melanogaste 185 bp (38 bp linker) in humans
ISWI complex models the spacingLinkers might have regulatory functions
The organization of nucleosomes on genes
Nucleosome numbering
The organization of nucleosomes on genes
Nucleosome numberingH2A.Z levels, acetylation, H3K4 methylation
and phasing
Nucleosome Positions
Independent positioningStatistical Positioning
Analog to Roulette wheel
Nucleosome-Free Region(NFR)
Poly(dA:dT) tracts contribute to rigidity We thought promoter regions would be
occluded by nucleosomes except when they were activated.
But in fact, NFRs demonstrated that open promoter states are stable and common, even at genes that are transcribed so infrequently.
Nucleosome-Free Region(NFR)
Low basal levels of leaky transcription might have a general housekeeping function
Open architecture of the 5' NFR is necessary for the initial 'pioneering' polymerase or whether transcription itself establishes the NFR from the closed state (after the last transcription)
Transcription start site selection by nucleosomes?
Most promoters seem to lack core promoter elements, including a TATA box, the TFIIB recognition element (BRE), INR, downstream promoter element (DPE) or motif ten element (MTE)
Control of DNA Access
DNA accessibility without catalysis thermal fluctuation energetically less favourable towards the midpoint of
the nucleosome Binding of one factor might stabilize a partially
disassembled state
Control of DNA Access
DNA accessibility without catalysisDNA accessibility and remodelling complexes
Control of DNA Access
DNA accessibility without catalysisDNA accessibility and remodelling complexesNucleosome eviction
Nucleosome dynamics define transcriptional enhancers. Nat Genet 42:343-347.
Genome-wide prediction of transcription factor binding sites using an integrated model. Genome Biol 11:R7.
Nucleosome Related TF Identification
Nucleosome Dynamics Define Transcriptional Enhancers
Monomethylated H3K4 (H3K4me) : enhancers, Trimethylated H3K4 (H3K4me3) :TSS, Dimethylated H3K4 (H3K4me2) : both the TSS and
enhancers
H3K4me2 are destabilized at AR binding site, but better positioning at flanking loci.
FOXA1 as pioneer factor to stabilize the nucleosomes.
Motif Analysis in the Paired Nucleosome Regions
Identify Nucleosome
Motif Analysis in the Paired Nucleosome Regions
Identify NucleosomeIdentify Enhancer Region
Motif Analysis in the Paired Nucleosome Regions
Identify NucleosomeIdentify Enhancer RegionMotif Analysis in Enhancer Region
Genome-wide prediction of transcription factor binding sites using an integrated model
Eight chromatin marks (H3, H3K4me1, H3K4me2, H3K4me3, H3K9me3, H3K36me3, H3K20me3, and H3K27me3)
Genome-wide prediction of transcription factor binding sites using an integrated model
Future work
Finding candidate nucleosome organizing factors
Better understand nucleosome positioning
Reference
I) NUCLEOSOME POSITIONING.II) NUCLEOSOME REMODELING. BCH 6415. http://www.med.ufl.edu/biochem/tyang/
http://www.uio.no/studier/emner/matnat/molbio/MBV4230/ Nucleosome dynamics define transcriptional enhancers, Nature
genetics 42 (4): 343-7, 2010 Apr Nucleosome positioning and gene regulation: advances through
genomics, Nature reviews. Genetics 10 (3): 161-72, 2009 Mar Inducible gene expression: diverse regulatory mechanisms,
Nature reviews. Genetics , 2010 Apr 27 Genome-wide prediction of transcription factor binding sites
using an integrated model, Genome biology 11 (1): R7, 2010 Jan 22
http://en.wikipedia.org/wiki/Histone
Q&A