Control of Gene Expression

Transcriptional control

Most common control point; molecules bind DNA or polymerase to regulate transcription

Pre-mRNA processing

Eukaryotes only; splicing, 5’ cap, 3’ poly-A tail affect transcript stability and translation

Translational control

Regulates efficiency of mRNA translation into protein

Protein activity regulation

Direct modification or ligand binding can activate/inhibit protein function

Protein degradation

Misfolded or unneeded proteins tagged with ubiquitin → destroyed by proteasome

Cis-regulatory elements

DNA sequences (promoter, operator, enhancer) that bind trans factors

Trans-regulatory factors

Proteins or RNA that bind cis elements to regulate transcription

Activator protein

Binds DNA or polymerase to increase transcription

Repressor protein

Binds DNA or polymerase to decrease transcription

Regulatory ligand

Small molecule or protein that binds regulatory protein and changes its conformation/function

Genetic switch

Group of regulatory proteins working together to turn gene(s) on/off or modulate expression

Tryptophan operon logic

Trp present → repressor active → transcription off; Trp absent → transcription on

Lac operon logic

Low glucose + lactose present → maximal transcription; Glucose high → CAP inactive → transcription low

Allolactose

Ligand that binds lac repressor → causes dissociation from operator → allows transcription

cAMP-CAP complex

Binds lac promoter when glucose is low → facilitates RNA polymerase binding

Polycistronic mRNA

Bacterial mRNA encoding multiple proteins from one transcript

Regulatory protein complexes

Often dimers or multimers; some subunits bind DNA, others act as coactivators/corepressors.

Positive vs negative control 

Activators increase transcription; repressors decrease transcription.

Eukaryotic transcription control

TFII factors, chromatin structure can block or allow access to genes; long-range regulation possible.

Integration of multiple influences 

Final gene output (“on”, “off”, or intermediate) is the result of combined regulatory effects.