Transcription Elongation & Termination

What is abortive initiation?

When the RNA falls off and transcription does not fully begin

What is crucial to maintaining RNA processivity?

DNA:RNA hybrid

What blocks the RNA exit channel?

Promoter DNA-binding proteins (Sigma factor/general TFs)

What occurs with each length of RNA?

• RNA <6 nt = abortive initiation

• RNA ~10nt = promoter clearance

• RNA ~20nt = elongation complex

What elongation factors help RNAP?

• TFIIS: transcript cleavage, suppresses pausing

• p-TEFb: phosphorylates CTD of Rpb1 subunit of RNAP II

What marks transcription elongation?

Phosphorylation of Serine 2 (by pTEFB) in the RNAP II C-terminal domain

What elongation factors promote movement through chromatin?

FACT: facilitates chromatin transcription

What occurs when a stalling RNAP backtracks?

• Transcription cleavage factors (TFIIS) can cut 3’ protruding RNA by enhancing endonuclease activity of RNAP

• RNAP has another chance to add correct nucleotide

What is an intrinsic terminator?

An RNA hairpin followed by a poly-U tract is used to terminate RNAP

What occurs in bacterial transcription termination?

Rho races up RNA (5’ → 3’) to reach RNAP, which disrupts the RNA-DNA hybrid

What is the torpedo model in eukaryotic transcription termination?

Rat1 (Xrn2) degrades RNA in 5’ → 3’ direction

What is the allosteric model in eukaryotic transcription termination?

A conformational change in RNAP releases it from DNA

What makes sure transcription doesn’t terminate early?

Y1 phosphorylation prevents premature recruitment of cleavage factors & tyrosine phosphorylation within RNAP II CTD is an anti-termination signal