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.

• 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

17.2 Changes in Chromatin Structure Affect the Expression of Genes

• Trancriptional activators, coactivators, and repressors

17.3 The Initiation of Transcription Is Regulated by Transcription Factors and Transcriptional

Activator Proteins

• Transcriptional activator protein GAL4

17.3 The Initiation of Transcription Is Regulated by Transcription Factors and Transcriptional

Activator Proteins

Concept Check 1

Most transcriptional activator proteins affect transcription by interacting with .

a. introns

b. the basal transcription apparatus

c. DNA polymerase

d. nucleosomes

Concept Check 1

Most transcriptional activator proteins affect transcription by interacting with .

a. introns

b. the basal transcription apparatus

c. DNA polymerase

d. nucleosomes

• 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

17.3 The Initiation of Transcription Is Regulated by Transcription Factors and Transcriptional

Activator Proteins

• 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

17.4 Some Genes Are Regulated by RNA Processing and Degradation

• 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

17.5 RNA Interference Is an Important Mechanism of Gene Regulation

• Model Genetic Organism

• The plant Arabidopsis thaliana

17.6. Some Genes Are Regulated by Processes That Affect Translation or by

Modification of Proteins