Prokaryotic vs eukaryotic gene organization

1. Prokaryotic transcriptional regulatory regions (promoters and operators) lie close to the transcription start site
2. Functionally related genes are frequently located near each other in prokayotes
3. These “operons” are transcribed into a single mRNA with internal translation initiation sites

Promoter controls transcription

-Efficiency of recruitment of polymerase determines
   frequency of initiation
-Expression further modulated by regulatory proteins

  

Eukaryotic gene expression regulation by genetic switches is more complex

-Eukaryotic gene transcription is regulated in three ways that are different from those in prokaryotes

    

     "Gene regulatory proteins can control transcription from a distance

     Gene activator proteins promote the assembly of transcriptional complexes

     Packaging of eukaryotic DNA in chromatin"

Eukaryotic pol II promoter

Assembly of initiation complex

-Many steps
-Promoters have different efficiencies


How do promoters differ?
- Promoter strength (recruitment of transcription complex)
- Upstream sequences that bind regulatory proteins

Eukaryotic positive regulation

-Activator works through “mediator” complex
-Activator also modifies chromatin

Inductive Gene Expression

Repressor binds operator site (overlaps with region bound by RNAP)
-no transcription
Absence of repressor, RNA polymerase binds weakly
-basal level expression
Inducer
-Cause production of enzymes to metabolize them
-Removal halts enzyme synthesis (transcription)