Regulation of Gene Expression

Page
7

Fig. 18-9-3

Enhancer

TATA

box

Promoter

Activators

DNA

Gene

Distal control

element

Group of

mediator proteins

DNA-bending

protein

General

transcription

factors

RNA

polymerase II

RNA

polymerase II

Transcription

initiation complex

RNA synthesis

Slide 44

Some transcription factors function as repressors, inhibiting expression of a particular gene

Some activators and repressors act indirectly by influencing chromatin structure to promote or silence transcription

Slide 45

A particular combination of control elements can activate transcription only when the appropriate activator proteins are present

Combinatorial Control of Gene Activation

Slide 46

Fig. 18-10

Control

elements

Enhancer

Available

activators

Albumin gene

(b) Lens cell

Crystallin gene

expressed

Available

activators

LENS CELL

NUCLEUS

LIVER CELL

NUCLEUS

Crystallin gene

Promoter

(a) Liver cell

Crystallin gene

not expressed

Albumin gene

expressed

Albumin gene

not expressed

Slide 47

Coordinately Controlled Genes in Eukaryotes

Unlike the genes of a prokaryotic operon, each of the coordinately controlled eukaryotic genes has a promoter and control elements

These genes can be scattered over different chromosomes, but each has the same combination of control elements

Copies of the activators recognize specific control elements and promote simultaneous transcription of the genes

Slide 48

Mechanisms of Post-Transcriptional Regulation

Transcription alone does not account for gene expression

Regulatory mechanisms can operate at various stages after transcription

Such mechanisms allow a cell to fine-tune gene expression rapidly in response to environmental changes

Slide 49

RNA Processing

In alternative RNA splicing, different mRNA molecules are produced from the same primary transcript, depending on which RNA segments are treated as exons and which as introns

Animation: RNA Processing

Slide 50

Fig. 18-11

or

RNA splicing

mRNA

Primary

RNA

transcript

Troponin T gene

Exons

DNA

Slide 51