Control of Gene Expression

Chapter 16Genes and Development

Proteins can determine the DNA sequence by binding the major groove of DNA.

Proteins binding the minor groove cannot determine the exact sequence of bases.

Prokaryotic gene regulation

Lac Operon

Prokaryotic gene regulation

Trp Operon

Biosynthesis of the amino acid typtophan

Therefore, the regulation is the opposite of the lac operon.

Eukaryotic gene regulation

Enhancer (DNA sequence)

Activator (protein)

Looping

1. Nucleosome sliding 2. Remodeled nucleosome

3. Nucleosome displacement 4. Histone replacement

ADP +ATP Pi

ATP -dependentremodeling factor

Cytoplasm

RNA Polymerase II

microRNA gene

Pri-microRNANucleus

Drosha

Exportin 5

Pre-microRNA

Dicer

Mature miRNA

RISC mRNA

RISC

mRNA cleavage

mRNA

RISC RISC

Inhibition of translation

RNA Polymerase II

microRNA gene

Pri-microRNANucleus

Drosha

Exportin 5

Pre-microRNA

Exogenous dsRNA, transposon, virus

P P

P P

P

PP

PsiRNAs

+Ago

RISC

Ago

RISC

siRNAin RISC

Cleavage of target mRNA

Repeated cuttingby dicer

mRNA

DNA

2. RNA splicing Gene expression can be controlled by altering the rate of splicing in eukaryotes. Alternative splicing can produce multiple mRNAs from one gene.

Mature RNA transciptExonsIntrons

5´ cap3´ poly-A tail

Cutintron

RNA polymerase II

3´

5´ Primary RNA transcript

1. Initiation of transcription Most control of gene expression is achieved by regulating the frequency of transcription initiation.

3. Passage through the nuclear membrane Gene expression can be regulated by controlling access to or efficiency of transport channels.

4. Protein synthesis Many proteins take part in the translation process, and regulation of the availability of any of them alters the rate of gene expression by speeding or slowing protein synthesis.

3´

5´

Smallsubunit

Nuclearpore

5´ capmRNA

Largesubunit

3´ poly-A tail

23

5. RNA interference Gene expression is regulated by small RNAs. Protein complexes containing siRNA and miRNA target specific mRNAs for destruction or inhibit their translation.

6. Posttranslational modification Phosphorylation or other chemical modifications can alter the activity of a protein after it is produced.

Completedpolypeptide

chain

RISC

P

P