Euakryotic Transcription

SWI/SNF complex

Uses ATP to slide or remove nucleosomes, making promoters accessible.

HATs (histone acetyltransferases)

Acetylate histones to loosen chromatin and activate transcription.

HDACs (histone deacetylases)

Deacetylate histones, causing chromatin condensation and repressing transcription

HMTs (histone methyltransferases)

add methyl groups to histones, which can repress transcription

TFIID

recognizes and binds the TATA box via its TBP (TATA binding protein)

TFIIA

stabilizes TFIID binding and assists in promoter recognition

TFIIB

• helps RNA pol II recognize the promoter and positions it correctly

• closely mimics sigma factor in prokaryotes

TFIIF

• escorts RNA pol II to the promoter and helps stabilize the transcription complex

TFIIE

• recuits TFIIH and helps in DNA melting at the transcription start site

TFIIH

• has helicase activity to unwind DNA and kinase activity

• phosphorylates C-terminal domain of RNA pol II for elongation

RNA pol I

transcribes rRNA in the nucleolus

RNA pol II

transcribes mRNA, miRNA, snRNA, and other non-coding RNAs

RNA pol III

transcribes tRNA

serine-5 phosphorylation

transition from initiation to elongation

TFIIE and TFIIH

• fall off from the initiation complex after promoter clearance

DSIF (DRB sensitivity inducing factor) and NELF (negative elongation factor)

temporarily pauses RNA pol II before productive elongation

P-TEFb (positive transcription elongation factor b)

Phosphorylates NELF, DSIF and Ser2 of RNA pol. CTD to resume elongation, recruits splicing and 3’ end processing factors

CPSF (cleavage and polyadenylation specificity factor)

recognizes polyadenylation signal (AAUAAA) and cleaves the RNA

CstF (cleavage stimulation factor)

helps RNA cleavage near the poly (A) signal

CPSF-73

cleaves the RNA at poly (A) signal

XRN2 exonuclease

(degrades extra RNA downstream of the cleavage site in 5’ → 3’