Transcription of EukaryotePromoters: - TATA box

- CAAT box (CCAAT box) - GC box

- ~ 200 bp upstrean of startpoint (mostly)

- work with RNA pol. / transcription factors

Enhancers:- stimulate initiation- ~ 100 bp- upstream / downstream- interact with

transcriptional factors

PROMOTERS:- TATA box (center at -30)- CAAT box (seq. at -75)- GC box ( seq. at -90); GGGCGG

Eukaryotic RNA polymerasesRNA pol. I rRNARNA pol. II mRNARNA pol. III tRNA & other small RNA

RNA Pol. I has a bipartite Promoters

Increase efficiency by the upstream control elements (UCE)

RNA pol. III uses both downstream and up stream ppromoters

TF IIIB ; Initiation factor / Positioning factorTF IIIA & TF IIIC ; Assembly factors

TBP = TATA box binding proteinTAFs = TBP-associated

factors

RNA Pol II requireATP hydrolysis (TF IIE) & helicase activity (TF IIH) for Pol. movement

A model of phosphorylationto release RNA Pol II from TF for elongation

222 5 3Fig. . Overview: Addition to the ’ and ’ ends,SSSSSSSS SS SSS SSS SSSSSSS

Two stages of splicing:

SSSSSS SSSSS. ; 5 ’ , SSSSSS -SSSS S SSS.

SSSS S SSSSSS 2 3nd st.; cut at ’ splice site,

release free intron, right exon ligated to

the left exon

SPLICING REACTION: by transesterification reaction;breaking and making of bonds

Cis-splicing trans-splicing reaction

tRNA splicing is different mechanism:

separate and ligate

tRNA splicing depends on a secondary structure rather than sequence of the intron

1st step: phosphodiester bond cleavage by endonuclease

2nd step: require ATP, bond formation by RNA ligase

Group I intron: Self-splicing by transesterification SSSSSSSS :

- a monovalent cation, a divalent cation,- a guanine nucleotide cofactor (only G), - 3musthave a ’ OHgroup

FIG.23.2 Self-splicing OR Autosplicing of Group I introns

Some introns code for Proteins:- Endonuclease- Reverse transcriptase- Muturase: for splicing

Fig. 23.11 Endonuclease:- make a double-strand break in DNA- duplicated-intron inserted at the break

Fig.23.12 Endonuclease / Reverse transcriptase

5’ END of eukaryotic mRNA is capped:- start with nucleoside triphosphate (purine A or G)- first nucleotide retains 5’ triphosphate group- addition of the 5’ terminal G catalyzed by a nuclear enz., guanylyl transferase- SSS SSS , SS SSSSSSS SSSSSSSSSSS , called CAP

3 ’ ENDS OF EUKARYOTIC mRNA- RNA Pol I & Pol III terminate like bact. RNA Pol- RNA Pol I; recognize of an 18 base termination seq.- RNA Pol III; recognize at the second U within a run of 4U bases- RNA Pol II; loosely specified by cleavage / polyadenylation - seq. AAUAAA locate from 11 to 30 nts upstream of poly A site / provide the signal for both cleavage / polyadenylation