TRANSCRIPTION IN EUKARYOTES

Eukaryotic transcription is carried out in the nucleus of the cell and proceeds in three sequential stages: initiation, elongation, and termination. Eukaryotes require transcription factors to first bind to the promoter region and then help recruit the appropriate polymerase.

1. TRANSCRIPTIONIN EUKARYOTES
Dr.Rachana Choudhary
(HOD , Microbiology)
SHRI SHANKARACHARYA MAHAVIDYALAYA
JUNWANI, BHILAI

2. CONTENTS
•INTRODUCTION
•Definition
•history
•Enzymes involved in transcription
•Transcriptional Factor
•MACHANISM OF TRANSCRIPTION IN EUKARYOTES:
-INITIATION
-ELONGATION
-TERMINATION
•DIFFERENT BETWEEN PROKARYOTIC & EUKARYOTIC TRANSCRIPTION
•Significance
•reference
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3. INTRODUCTION
Transcription,orRNASynthesis,istheprocessof
creatingRNA,copyofasequenceofDNA.
BothRNAandDNAarenucleicacids,which
usebasepairsofnucleotidesasacomplementary
languagethatcanbeconvertedfromDNAtoRNA
inthepresenceofthecorrectenzymes.
Duringtranscription,aDNAsequenceisread
byRNApolymerase,whichproduces a
complementary,RNAstrand.
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4. definition
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Transcription is a process in which a DNA strand provides
the information for the synthesis of RNA strand, in the
presence of DNA dependent RNA polymerase.

5. history
•Central dogma was proposed by Crick in 1958.
•The existence of mRNA was shown by Spiegel man and
coworkers in 1961.
•Activity of RNA polymerase was discovered by Werrin
1960.
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6. CHARACTERISTICS RNA POL IRNA POL IIRNA POL III
Location NucleolusNucleoplasmNucleoplasm
Target gene r RNA genemRNA genest RNA
55 r RNA
Promoters Upstream of
the start
point
Upstream of
the start point
Downstream of
the start point
Activity 5-70 % 20-40 % ~10%
Enzymesinvolvedintranscription

7. Eukaryotic RNAPs
Inbacteria,allmRNAismadefromthesameRNA
polymerase.However,ineukaryotes,thereareThree
DifferentRNAPolymerases.
1.RNA Polymerase Isynthesizes rRNA.
2.RNA Polymerase IIsynthesizes all Protein Coding
Genes & mRNA.
3.RNA polymerase III synthesizes t RNAs and also
snRNAs (small nuclear RNAs) and small cellular
RNAs.
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8. Transcriptional factors
There are three types of transcriptional factors
(i) Basal
(ii) Upstream factor
(iii) Regulatory transcriptional factor
(i)BASAL:-Theyarerequiredforinitiationatallthepromoters.
TheyjoinRNAPolymeraseIItoformacomplexaroundStart
Point.Therearedifferentbasalfactorstheyareasfollows:-TF
IIA,TFIIB,TFIID,TFIIF,TFIIH,TFIII.
(ii)UPSTREAM FACTOR:-Theyincreasethefrequencyof
initiation.e.g.SPI.
(iii)REGULATORY TRANSCRIPTION FACTOR:-Theyare
producedasactivatedatspecifictimeastissue.Theycontrol
transcriptionoftheconcernedgene.
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9. EUKARYOTIC TRANSCRIPTION PROCESS
The three step involved in transcription:-
1.Initiation
2. Elongation
3. Termination
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10. TRANSCRIPTION IN EUKARYOTES
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11. Initiation
Ineukaryotes,theinitiationoftranscription,requiresthe
presenceofacorepromotersequenceintheDNA.
PromotersareregionsofDNAwhichpromotetranscription
andarefoundaround-10to-35basepairsupstreamfrom
thestartsiteoftranscription.Corepromotersaresequences
withinthepromoterwhichareessentialfortranscription
initiation.RNApolymeraseisabletobindtocore
promotersinthepresenceofvariousspecifictranscription
factors.

12. •ThemostcommontypeofcorepromoterineukaryotesisashortDNA
sequenceknownasaTATAbox.TheTATAbox,asacorepromoter,is
thebindingsiteforatranscriptionfactorknownasTATAbinding
protein(TBP),whichisitselfasubunitofanothertranscriptionfactor,
calledTranscriptionFactorIID(TFIID).
•Onetranscriptionfactor,DNAhelicase,hashelicaseactivityandsois
involvedintheseparatingofopposingstrandsofdouble-strandedDNA
toprovideaccesstoasingle-strandedDNAtemplate.
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13. ELONGATION
Whenthetwostrandsgetseparateda
transcriptionalbubbleisformedandsynthesisof
RNAbeginsfrom5’-3’end.Asthetranscription
bubblemovesalongthestrandssynthesisofmRNA
proceed.
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14. Eukaryotic RNA Termination
Transcriptionterminationineukaryotesislessunderstood
butinvolvescleavageofthenewtranscriptfollowedby
template-independentadditionofAsatitsnew3'end,ina
processcalledpolyadenylation.
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16. MATURATION OF RNA
•In eukaryotes, the RNA is processed at both ends before
it is spliced.
•At the 5‘ end, a cap is added consisting of a modified
GTP (guanosine triphosphate). This occurs at the
beginning of transcription. The 5' cap is used as a
recognition signal for ribosomes to bind to the mRNA.
•At the 3' end, a poly(A) tail of 150 or more adenine
nucleotides is added. The tail plays a role in the stability
of the mRNA.
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17. DIFFERENT BETWEEN PROKARYOTIC & EUKARYOTIC
IN PROKARYOTES
•DNA dependent RNA
Polymerase-RNAPs.
•Promoter sequences-
TATpuATpu located -10 bp
of upstream.& TTGACA
Located -35 bp upstream.
•Post transcriptional changes
is none. Transcription and
translation takes place
simultaneously.
•Transcription factors not
required.
IN EUKARYOTES
•DNA dependent RNA
Polymerase-I,II,III.
•Promoter sequences-TATA
box Located-30bp
upstream.& CAAT box
Located -70 to -80bp
upstream.
•Co transcription and post
transcription change
present.
•Transcription factors
required.

18. •ThesinglestrandedintermediaryRNAmolecule
appropriatelyreferredtoasamRNAisderivedfromDNA
bythisprocess.
•OnlyoneofthetwostrandsofDNAgivesrisetoa
meaningfulRNAproduct.
•OnemoleculeofDNAwillgiverisetoseveralmolecules
ofRNA,whicharereleasedfromDNAtemplates.

19. Reference
GENESIX;BenjaminLevin;jones&Bartlett
Publishers,2006.
B.D.Singh–FundamentalGenetic4
th
Edition(2006)
Dubey& Maheshwari–Microbiology
S. Mahesh –Molecular Biology & Biophysics
P.K. Gupta –Cell And Molecular Biology 2
nd
Edition
(2003)
Lansing M. Prescott –Microbiology 6
th
Edition
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