Eukaryotic transcription (2)

Gene expression is dependent on…

transcription rate (73%) and mRNA degradation (11%)

Transcription

rNTP instead of dNTP bc DNA→RNA

Why is polymerization energetically favoured?

High E bond between alpha and beta P replaced by Low E phosphodiester bond

Promoter

1. Upstream

2. Info for Pol to start transcription at the right site

Start site (+1)

RNA Pol places its 1st phosphodiester bond to the right of the arrow

Coding sequence

1. Downstream

2. Includes starting code

Primary RNA transcript (5-3)

RNA Pol II generates it from template strand (3-5 and rate=1000-3000 nt/min)

Non template strand

Coding strand

Initiation

RNA Pol bonds, denature and catalyzes PP linkage

Elongation

RNA Pol advances 3’→5’

Termination

Stop site (termination sequence) recognized

Similarity in prokaryotic and eukaryotic transcription

Eukaryotes need intermediate like promoter to guide RNA Pol II : sigma factors, cAMP site

Difference in prokaryotic and eukaryotic transcription

Eukaryotes have monocistronic mRNA vs polycistronic

RNA Pol in eukaryotes

Pol I, II and III

RNA Pol I activity

Completely inhibited by amanitin bc it binds to its active site

RNA Pol I transcribes…

Pre-rRNA

RNA Pol II transcribes… (4)

mRNA, small nuclear RNA (splicing), small interfering RNA, micro RNA

RNA Pol III transcribes…

tRNA, 5S rRNA, snRNA U6, 7S RNA

Clamp

Changes conformation during elongation stage

Similarities in RNA Pols

Common subunits (which are similar to prokaryotic ones)

CTD

Carboxyl terminal domain: heavily repeated (min 10X) and unstructured (bc terminal)

Phosphorylation of CTD

Active transcription