Transcript 17.2 Changes in Chromatin Structure Affect the Expression of Genes

17.1 Eukaryotic Cells and Bacteria Have Many
Features of Gene Regulation in Common, but
They Differ in Several Important Ways
• Each structural gene has its own promoter, and
is transcribed separately.
• DNA must unwind from the histone proteins
before transcription.
• Activators are more common in Eukaryotes.
• Transcription and translation are separated in
time and space.
17.2 Changes in Chromatin Structure
Affect the Expression of Genes
• DNase I hypersensitivity
• DNase I hypersensitive sites: more open
chromatin configuration site, upstream of the
transcription start site
• Histone modification
• Addition of methyl groups to the histone
protein tails
• Addition of acetyl groups to histone proteins
17.2 Changes in Chromatin Structure
Affect the Expression of Genes
• Chromatin remodeling
• Chromatin-remodeling complexes: bind
directly to DNA sites and reposition
nucleosomes
• DNA methylation of cytosine bases adjacent
to guanine nucleotides (CpG)–CpG islands
17.3 The Initiation of Transcription Is Regulated
by Transcription Factors and Transcriptional
Activator Proteins
• Trancriptional activators, coactivators, and
repressors
17.3 The Initiation of Transcription Is Regulated
by Transcription Factors and Transcriptional
Activator Proteins
• Transcriptional activator protein GAL4
Concept Check 1
Most transcriptional activator proteins affect
transcription by interacting with
.
a.
b.
c.
d.
introns
the basal transcription apparatus
DNA polymerase
nucleosomes
Concept Check 1
Most transcriptional activator proteins affect
transcription by interacting with
.
a.
b.
c.
d.
introns
the basal transcription apparatus
DNA polymerase
nucleosomes
17.3 The Initiation of Transcription Is Regulated
by Transcription Factors and Transcriptional
Activator Proteins
• Enhancers and insulators
• Enhancer: DNA sequence stimulating
transcription from a distance away from
promoter
• May increase transcription of many genes in
vicinity
• Insulator: DNA sequence that blocks or
insulates the effect of enhancers
17.3 The Initiation of Transcription Is Regulated
by Transcription Factors and Transcriptional
Activator Proteins
• Coordinated gene regulation
• Response elements: common regulatory
elements upstream of the start sites of a
collective group of genes in response to a
common environmental stimulus
• Heat-shock proteins
17.4 Some Genes Are Regulated by RNA
Processing and Degradation
• Gene regulation through RNA splicing
17.4 Some Genes Are Regulated by RNA
Processing and Degradation
•
The degradation of RNA
•
5′-cap removal
•
Shortening of the poly(A) tail
•
Degradation of 5′ UTR, coding sequence,
and 3′ UTR
17.5 RNA Interference Is an Important
Mechanism of Gene Regulation
• Small interfering RNAs and microRNAs
• RISC: RNA-induced silencing complex
17.5 RNA Interference Is an Important
Mechanism of Gene Regulation
• Mechanisms of Gene regulation by RNA
interference
• RNA cleavage: RISC containing an siRNA,
pair with mRNA molecules and cleavage to
the mRNA
• Inhibition of translation
• Transcriptional silencing: altering chromatin
structure
• Silencer-independent degradation of mRNA
17.6. Some Genes Are Regulated by
Processes That Affect Translation or by
Modification of Proteins
• Model Genetic Organism
• The plant Arabidopsis thaliana