transcription in eukaryotes, by saswat kumar mohanty. from pondicherry university
TRANSCRIPT
MOLECULAR BIOLOGY (BMB-414)
SEMINAR ON :EUKARYOTIC TRANSCRIPTIONSEMINAR BY :SASWAT KUMAR MOHANTYMSc BMB 2ND SEM. REG.NO. : 14368037
DIFFERENT TYPES OF RNA POLYMERASE
3 TYPES OF RNA POLYMERASE
1. RNA POLYMERASE -I
2. RNA POLYMERASE -II
3. RNA POLYMERASE –III
ALL ARE DISTINCT COMPLEXS BUT HAVE CERTAIN SUBUNIT IN COMMON
EACH POLYMERASE HAS SPECIFIC FUNCTION
RNA POLYERASE- IRESIDES IN THE NUCLEOLUS
SYNTHESIZED- 28srRNA , 18srRNA & 5.8srRNA
CONTAIN 14 SUBUNITS
RNA POLYMERASE : IIFOUND IN NUCLEOPLASM
SYNTHESIZES PRECURSORS TO MESSENGER RNA
ALSO SYNTHESIZES SMALL NUCLEOLAR RNA
CONTAINS 12 SUBUNITS
RNA POLYMERASE: IIIFOUND IN NUCLEOPLASM
SYNTHESIZES TRANSFER RNA, 5SrRNA
CONTAIN 17 SUBUNITS
TRANSCRIPTIONPROTEIN
NO. OF SUBUNITS
FUNCTION
POL : II 12 CATALYZES RNA SYNTHESIS
TBP 1 SPECIFICALLY RECOGNIZES THE TATA BOX
TFIIA 3 STABILIZES BINDING OF TFIIB AND TBPNTO THE PROMOTER
TFIIB 1 BINDS TO TBP, RECRUITS POLII-TFIIF COMPLEX
TFIIE 2 RECRUITS TFIIH, HAS ATPase AND HELICASE ACTIVITIES
TFIIF 2 BINDS TIGHTLY TO POL II, BINDS TO TFIIB & PREVENTS BINDING OF POL II TO NONSPECIFIC DNA SEQUENCE
TFIIH 12 UNWIND DNA AT PROMOTORPHOSPHORYLASE POLII WITHIN CTD
ELLPTEFBTFIIS
PHOSPHORYLATES POLII WITHIN CTD
THREE CLASSES OF PROMOTERS ARE FOUND IN EUKARYOTIC NUCLEAR GENES, ONE FOR EACH TYPE OF RNA POLYMERASEPRMOTER FOR RNA POL. I
PRODUCE PRECURSOR FOR 3 LARGEST RIBOSOMAL RNA
THREE CLASSES OF PROMOTERS ARE FOUND IN EUKARYOTIC NUCLEAR GENES, ONE FOR EACH TYPE OF RNA POLYMERASEPRMOTER FOR RNA POL. II
TATA DRIVEN PROMOTERDPE DRIVEN PROMOTER
THREE CLASSES OF PROMOTERS ARE FOUND IN EUKARYOTIC NUCLEAR GENES, ONE FOR EACH TYPE OF RNA POLYMERASERNA POLYMERASE III
RNA POLYMERASE II FORMS A PRE-INITIATION COMPLEX WITH GENERAL TRANSCRIPTION AT THE PROMOTER
RNA POLYMERASE II FORMS A PRE-INITIATION COMPLEX WITH GENERAL TRANSCRIPTION AT THE PROMOTER
RNA POLYMERASE II FORMS A PRE-INITIATION COMPLEX WITH GENERAL TRANSCRIPTION AT THE PROMOTER
RNA POLYMERASE II FORMS A PRE-INITIATION COMPLEX WITH GENERAL TRANSCRIPTION AT THE PROMOTER
ABORTIVE INITIATION1.FORMATION OF RNA POL. – PROMOTER COMPLEX
2.RNA POL. UNWINDS 1 TURN OF DNA SRROUNDING THE TRANSCRIPTION STATRT SITE TO YIELD AN RNA POL- PROMOTER OPENCOMPLEX
3.RNA POL ENTERS IN TO ABORTIVE CYCLE---- RELEASE SHORT RNA PRODUCT ( 10 NUCLEOTIDE)
4.RNA POL ESCAPE THE PROMOTER & ENTERS IN TO ELONGATION STEP OF TRANSCRIPTION
DNA SCRUNCHING
PROMOTER CLEARANCE TRANSCRIPT ATTAINS THE THRESHOLD LENGTH OF 10 NUCLEOTIDE, IT ENTERS THE
RNA EXIT CHANNEL
RNA POL BREAKS IT INTERACTIONS WITH THE PROMOTER ELEMENTS AND ANY REGULATORY PROTEINS ASSOCIATED WITH THE INITIATION COMLEX THAT IT NO LONGER NEEDS.
CTD OF POL II CONTAINS SERIES OF REPEAT OF THE HEPTADE SEQUENCE --- Tyr-Ser-Pro-Thr-Ser-Pro-Ser.
EACH SITE CONTAINS SITES FOR PHOSPHORYLATION BY SPECIFIC KINASES INCLUDING 1 i.e A SUBUNIT OF TFIIH
CDK9, WHICH IS A PART OF THE COMPLEX pTEFb (POSITIVE TRANSCRIPTION ELONGATION FACTOR b ) PHOSPHORYLATES CTD, PRIMARILY ON THE Ser RESIDUE OF THE CTD REPEAT SEQUENCE.
ELONGATIONRNA POL MOVES ALONG THE DNA AND MAKES A RNA COPY OF
DNA TEMPLET STRAND .
FOR EVERY DNA BASE PAIR SEPARATED BY THE ADVANCING POLYMERASE , ONE HYBRID RNA:DNA BASE PAIR IS IMMEDIATELY FORMED
DNA STRANDS AND NASCENT RNA CHAIN EXIT FROM SEPARATE CHANNELS.
2 DNA STRANDS REUNIT AT THE TRAILING END OF THE TANSCRIPTION BUBBLE WHILE SINGLE STRAND RNA EMERGES ALONE
ELONGATION CONTINUE..ELONGATION FACTORPTEFb – PHOSPHORYLATES 2ND RESIDEUE Ser OF CTD REPEATS OF
BOUND POL II
PTEFb ALSO PHOSPHORYLATES AND ACTIVATES SPT5 AND TAT-SF1.
SPT5- UNIVERSAL TRANSCRIPTION FACTOR HELPS RECRUIT 5’-CAPPING ENZYME TO POL II & CTD PHOSPHORYLATES AT Ser-5
TAT-SF1 RECRUITS COMPONENTS OF THE RNA SPLICING MACHINARY TO THE Ser-2 PHOSPORYLATED CTD.
PAUSING, POISING & BACKTRACKING
PAUSING IS MEDIATED BY A COMPLEX CALLED
NELF(NEGATIVE ELONGATION FACTOR) IN
COLLABORATION WITH DSIF ( DRB SENSITIVE INDUCING FACTOR CONTAINING SPT4/SPT5)
BLOCKAGE IS RELEASED ONCE POLYMERASE RECEIVE ACTIVATION SIGNAL SUCH AS PHOSPHORYLATION OF Ser-2 OF CTD TAIL BY PTEFb.
NOT A SMOOTH RIDE ON A DNA RAILWAY
TERMINATIONLAST STAGE OF TRANSCRIPTION
LEADS TO DISSOCIATION OF COMPLETE TRANSCRIPT & RELEASE OF RNA POLYMERASE FROM THE TEMPLETE DNA
TERMINATION CONTINUE…FACTOR DEPENDENT TERMINATION FOR RNA POL I ----- EUKARYORIC CELL CONTAIN
HUNDREDS OF RIBOSOMAL DNA REPEATS.
TERMINATION OCCURS IN RIBOSOMAL INTERGENIC SPECER REGION THAT CONTIN SEVERAL TRANSCRIPTION TERMINATION SITE UPSTREAM OF POL I PAUSING SITE.
3’ END CLEAVED GENERATING A LARGE PRIMARY RIBOSOMA RNA i.e. FURTHER PROSSED IN TO THE MATURE 18S,5.8S,&28S RIBOSOMAL RNA
TERMINATION CONTINUE…FACTOR DEPENDENT TERMINATION
TERMINATION CONTINUE…FACTOR DEPENDENT TERMINATION AS POL II RECHES THE END OF A GENE, 2 PROTEIN
COMPLEX CARRIED BY CTD - CPSF ( CLEAVAGE &
POLYADENYLATION SPECIFICITY FACTOR)& CSTF ( CLEAVAGE STIMULATION FACTOR ), RECOGNISE THE POLY-A SIGNAL IN THE TRANSCRIBED RNA.
POLY –A BOUND CPSF AND CSTF RECRUIT OTHER PROTEINS TO CARRY OUT RNA CLEAVAGE AND POLYADENYLATION
TERMINATION CONTINUE…FACTOR DEPENDENT TERMINATION
TWO MODEL
1. ALLOSTERIC MODEL
2. TORPEDO MODEL
FACTOR – INDEPENDENT TERMINATIONPOL III TERMINATION SIGNAL CONSISTS OF A STRETCH OF
THYAMINS LOCATED WITHIN 40BP DOWNSTREAM FROM THE 3’ END OF MATURE RNAs.
THIS POLY T TERMINATION SIGNAL PAUSES PO II AND CAUSES IT TO BACK TRACK TO THE NEAREST RNA HAIR PIN TO BECOME A DEAD-END COMPLEX.
HAIR IN ALLOSTERICALLY OPENS POL III
REFFERENCELEHNINGER PRINCIPLES OF BIOCHEMISTRY, FIFTH EDITION –
DAVID
THE WORLD OF THE CELL, 6TH EDITION, BY BECKER,KLEINSMITH & HARDIN
www.ncbi.nm.nih.gov/books/NBK9935
MOLECULAR BIOLOGY OF THE GENE, 5TH EDITION- WATSON
en.wikipedia.org/wiki/Abortive_initiation