biol 3301 - genetics ch20 - regulation of gene expression in eukaryotes st

8/18/2019 BIOL 3301 - Genetics Ch20 - Regulation of Gene Expression in Eukaryotes St

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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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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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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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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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3 )est stu"ie" complex of proteins that

remo"el chromatin 4 S6I8S


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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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&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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5e1el

DA sites in1ol1e" in regulation of

transcription


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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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%< 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

biol 3301 - genetics ch20 - regulation of gene expression in eukaryotes st

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