A chromatin template
In bacteria, transcription acts on a DNA template; in eukaryotes it acts on chromatin, whose structure must be opened before RNA polymerase can bind to the promoter.
Unlike bacterial transcription
Factors find the promoter
Bacterial RNAP can read the DNA sequence to find the promoter; a eukaryotic RNAP cannot. Basal transcription factors bind first, and the polymerase then binds the factor–DNA complex at the core promoter.
Three polymerases
Bacteria have a single type of RNAP. Eukaryotes have three: RNAP I makes rRNA (but not 5S rRNA), RNAP II mRNA and some small RNAs, and RNAP III tRNA, 5S rRNA and other small RNAs.
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Scene · 6 steps
Three RNA polymerases
Their many subunits, the ones they share, what RNAP II has in common with the bacterial enzyme, what it lacks, and its tail of repeats.
Play ↗ Scene · 6 stepsInactive, poised and active genes
Closed chromatin opening, the basal apparatus assembling in order at a poised gene, a second signal from an enhancer, and RNAP II leaving the promoter to transcribe the gene.
Play ↗ Scene · 6 stepsTBP and the TATA box
How the TATA-binding protein binds in the minor groove, sits astride the DNA like a saddle and bends it by about 80°.
Play ↗ Scene · 7 stepsEnhancers
How the DNA loops so an enhancer's activators reach the promoter: from near or tens of kilobases away, upstream or downstream, either way round; and the factors involved.
Play ↗ Scene · 7 stepsDNA methylation
5-methylcytosine at CpG sites, CpG islands at promoters, methylation kept through replication and added de novo, TET enzymes starting its removal, and the pattern of an active gene.
Play ↗ Library · 19 proteinsThe proteins, one by one
The three polymerases, the basal transcription factors, the nucleosome and the DNA methylation enzymes, each in 3D with its facts.
Open ↗ ReadingThe notes
Eukaryotic transcription in full: polymerases, promoters, the basal apparatus, TBP, enhancers and DNA methylation.
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