Regulation of Gene Expression

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Inherited mutations in the tumor-suppressor gene adenomatous polyposis coli are common in individuals with colorectal cancer

Mutations in the BRCA1 or BRCA2 gene are found in at least half of inherited breast cancers

Slide 114

Fig. 18-23

Slide 115

Fig. 18-UN1

Operon

Promoter

Operator

Genes

RNA

polymerase

Polypeptides

A

B

C

C

B

A

Slide 116

Fig. 18-UN2

Promoter

Genes

Genes not expressed

Inactive repressor:

no corepressor present

Corepressor

Active repressor:

corepressor bound

Genes expressed

Operator

Slide 117

Fig. 18-UN3

Promoter

Genes

Genes not expressed

Active repressor:

no inducer present

Inactive repressor:

inducer bound

Genes expressed

Operator

Fig. 18-UN2

Slide 118

Fig. 18-UN4

• Genes in highly compacted

chromatin are generally not

transcribed.

Chromatin modification

• DNA methylation generally

reduces transcription.

• Histone acetylation seems to

loosen chromatin structure,

enhancing transcription.

Chromatin modification

Transcription

RNA processing

Translation

mRNA

degradation

Protein processing

and degradation

mRNA degradation

• Each mRNA has a

characteristic life span,

determined in part by

sequences in the 5 and

3 UTRs.

• Protein processing and

degradation by proteasomes

are subject to regulation.

Protein processing and degradation

• Initiation of translation can be controlled

via regulation of initiation factors.

Translation

or

mRNA

Primary RNA

transcript

• Alternative RNA splicing:

RNA processing

• Coordinate regulation:

Enhancer for

liver-specific genes

Enhancer for

lens-specific genes

Bending of the DNA enables activators to

contact proteins at the promoter, initiating

transcription.

Transcription

• Regulation of transcription initiation:

DNA control elements bind specific

transcription factors.

Slide 119

Fig. 18-UN5

Chromatin modification

RNA processing

Translation

mRNA

degradation

Protein processing

and degradation

mRNA degradation

• miRNA or siRNA can target specific mRNAs

for destruction.

• miRNA or siRNA can block the translation

of specific mRNAs.

Transcription