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Regulation Of Gene Expression
In EukaryotesFeatures Prokaryotes Eukaryotes
Amount of geneticinformation
Much more
Chromosome organization Some proteins Complex of DA! histones! proteins
ucleus an" othercompartments
none Dou#le$mem#rane #oun"
um#er of chromosomes one Many linear
%ranscription an" translation o separation Spatially an" temporallyseparate"
mRA transcripts ot processe" &rocesse" #efore transportto cytoplasm! mRA moresta#le
um#er of cells! tissues unicellular multicellular
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Cloning of a frog from a skin cellElegant experiments in Xenopus
laevis #y 'ohn Gur"on! follo(ing
earlier experiments in
Rana temporaria #y )riggs an"
*ing +,-./0! pro1i"e" strong
e1i"ence that the genetic content
of "ifferentiate" somatic cells is
essentially unchange" from that
of the early em#ryo2
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Dolly %he Sheep
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Regulation Of Gene Expression
In Eukaryotes3 Regulation in the nucleus
4 Chromatin organization le1el 4 chromatin
remo"eling 4 DA le1el 4 controlle" transcription
4 RA le1el 4 alternate splicing
3 Regulation in cytoplasm 4 RA le1el 4 sta#ility
4 &olypepti"e le1el $ compartmentalization
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Regulation On %ranscriptional
5e1el
6hether a particular gene can #e
transcri#e" an" ho( often
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Regulation On %ranscriptional
5e1el
Organization of DA in the nucleus
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Gene Acti1ity Regulation at the
Chromosomal Organization 5e1el3 Structure of chromatin is the ma7or s(itch on8off
3 %ranscriptionally acti1e genes on the chromosome
are cycle" to the e"ge of the chromosome territory
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Gene Acti1ity Regulation at the
Chromosomal Organization 5e1el3 ucleus 4 highly organize"
3 A chromosome territory
4 gene "ense chromosomes more internal9
4 interchromosomal compartments
4 Rearrangements of chromosomal structure
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Regulation On %ranscriptional
5e1el
Chromatin Remo"eling
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Regulation at Chromatin
Remo"eling 5e1el3 :eterochromatin 4 transcriptionally inacti1e
3 Euchromatin 4 sensiti1e to Dase I "igestion!
transcriptionally acti1e3 Chromatin remo"eling;
4 Change in interaction #et(een DA an" histones
4 Remo"eling "one #y "i1erse group of proteins (ith
A%&ase acti1ity
4 After remo"eling! promoters #ecome accessi#le for
proteins
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:istone Co"e
3 Acetylation
3 Methylation
3 &hosphorylation
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%he :istone Co"e3 Methylation of histone (or of DNA)
usually turns a gene off
3 Acetylation of histone usually turns a
gene on
3 Phosphorylation -- we're not sure what
that does
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:istone Co"e
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Chromatin Remo"eling
3 Methyl groups can #e a""e" to lysine an"arginine 4 gene inacti1ation
3 &hosphate groups a""e" to hy"roxyl groupsof serine an" histi"ine intro"ucing anegati1e charge 4 chromatin unpackaging"uring replication
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ucleosome Altering
3 ucleosome altering can #e "one #y;
4 Altering the contacts #y DA an" histones
4 Mo1ing DA off nucleosomes
4 ucleosome core particle altere"! pro"ucing a
nucleosome "imer
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Chromatin Remo"eling
3 )est stu"ie" complex of proteins that
remo"el chromatin 4 S6I8S
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Chromatin Remo"eling
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:istone Mo"ification
3 Another mechanism of chromatin alteration
3 Catalyze" #y histone acetyl transferase
+:A%0 4 4 acetate group a""e" to #asic amino aci"s on
histone tail
4 Attraction #et(een #asic amino aci"s an" aci"icDA is lessene"
4 Remo"eling mo1es from promoter totranscription unit +co"ing region0
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:A%8:DAC
3 :A%s are targete" to genes #y specificacti1ator proteins
3 Can #e re1erte" 4 histone "eacetylase :DAC 4 co$repressors! remo1e acetyl groups
3 Insulator elements 4 short DA se=uencesthat #in" specific proteins an" act as #arriersthat pre1ent the sprea" of remo"eling intoneigh#oring genes
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Regulation On transcriptional
5e1el
%ranscriptional
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Regulation of %ranscription;
&roteins In1ol1e"3 &roteins in1ol1e" in control of transcription
4 transcription factors! %
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Regulation of %ranscription;
&roteins In1ol1e"3 %
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DA )in"ing Domains
3 DA #in"ing "omain 4 characteristic >$D
patterns or motifs;
4 :elix$turn$helix
4 ?inc finger
4 )asic leucine zipper +#?I&0
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Structural motifs (ithin "ifferent
types of transcription factors
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DA )in"ing Domain Motifs
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%rans$acti1ating Domain
3 %ranscription factors also contain a trans$
acti1ating "omains that interact (ith #asal
transcriptional complex 4 Different from DA$#in"ing "omain
4 Interact (ith other %
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Regulation On %ranscriptional
5e1el
DA sites in1ol1e" in regulation of
transcription
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Regulation of %ranscription;
DA Se=uences In1ol1e"3 cis$acting regulatory se=uences
4 &romoters
4 Enhancers
4 Silencers
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Align!ent of !ultiple
pro!oters
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Strong86eak &romoters
3 %he more similarity to a consensus
%A%AA%! the stronger promoter
3 5ess similarity 4 lo(er le1el of transcription
3 p mutation makes it stronger
3 Do(n mutation makes it (eaker
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I"entifying promoter se=uences
re=uire" for transcription
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Enhancers3 Similar to operator in prokaryotes! in eukaryotes;
4 Act o1er relati1ely large "istance 4 remote control
4 &osition not fixe" 4 can #e upstream! "o(nstream
4 Orientation can #e in1erte" 4 nspecific enhancementF
3 Difference from promoters; 4 &romoters gi1e #asal le1el of transcription
4 Enhancers pro1i"e full le1el transcription 4 Responsi#le for time an" tissue specificity
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Enhancers
3 Enhancer (ithin gene;
4 Immunoglo#ulin hea1y chain! in an intron
#et(een t(o exons
3 Enhancer "o(nstream
4 )eta$glo#in gene in humans
4 %hymi"ine kinase in chicken
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Enhanceosome
3 Acti1ators A E H enhanceosome
3 Gene$specific transcriptional s(itches
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%ranscriptional acti1ators #oun"
at "istant sites can influence gene
expression
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Regulation of %ranscription;
%< in %ranscription Initiation3 %ranscription complex assem#ly on
promoter
3 %ranscription factors are "ifferent for"ifferent RA polymerases
3 RA polymerases
4 RA& I 4 r RA 4 RA& II 4 mRA! snRAs
4 RA& III 4 tRA! .SRA
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RA &olymerase II
3
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&IC
3 % %A
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&IC
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Silencers
3 Gene silencing 4 transcriptionally silent
3 Silencers 4 DA se=uences that me"iate
this process
3 Specific protein complex that pre1ent
#in"ing (ith transcriptional enzymes
3 &ositional effect
3 RAi
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Regulation At DA Replication
5e1el$ Methylation3 DA methylation
3 DA mo"ification #y methylation of phosphates
an" sugars3 )ase methylation 4 C:> to cytosine
3 /$@J of Cs are methylate"
3 Extent of methylation is tissue specific
3 Degree of methylation H "egree of expression
3 Methylation patterns are tissue specific an"herita#le
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DA Methylation3 KBJ of #ase pairs are G$C
4 .L$mCpG 4>L
>L$GpCm$.L 4 mCpG is not "igeste" #y methyl sensiti1e
en"onucleases3 CpG islan"s 4 ,$/ k# long! >B!BBB in human
genome! near transcription sites
4 o methylation of Cs
4 DA is hypersensiti1e to DaseI
4 Contain less :, histone
E i f th IS% i
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Expression of the IS% gene in
the inacti1e chromosome of
human females
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DA Methylation an" Imprinting
3 Methylate" DA is transcriptionally represse"
4 :uman $chromosome is extensi1ely methylate"
4 %(o proteins kno(n to #in" to methylate" DA3 Methylation is controlle" #y parental origin 4
imprinting
4 If methylate" in mother! only allele of motherLs
chromosome (ill #e methylate"
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&rocessing 5e1el Control
Alternati1e Splicing
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Regulation at mRA 5e1el 4
Alternati1e Splicing3 Alternati1e splicing pro"uces many "ifferent
2
3 Examples; 4 %issue specific gene expression;
3 Calcitonin or CGR& +Calcitonin Gene Relate" &epti"e0+hormones0 in the calcitonin gene transcript from rats"epen"ing on tissue type
3 Alpha$tropomyosin
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%ropomyosin
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Sex In Drosophila
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%ranslational 5e1el Control
Determine (hether a particular
mRA is actually translate" an" ho(
often! for ho( long
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%ranslational 5e1el Control
3 %Rs contain nucleoti"e se=uences use" #y
the cell to me"iate translational le1el control
3 Cytoplasmic localization of mRA isgo1erne" #y >L %R 4 zip co"es
3 Motor proteins recognize them as tracks!
transport mRA to particular location3 Microfilaments anchor mRAs
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Cytoplasmic Control Of mRA
Sta#ility3 mRA 4 ri#osomesNsynthesis "egra"ation
+control point0
3 mRA longe1ity 4 &oly+A0 tail sta#ilizes mRA
4 Se=uence of >L%R 4 AA are short li1e"
4 Chemical factors 4 hormones 4 siRAs! miRAs lea" to mRA "egra"ation
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mRA "egra"ation in
mammalian cells
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RA Interference
3 Gene silencing #y "egra"ing mRA
through RAi mechanism