BSC 219

10/30/12

Eukaryotic gene regulation

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

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

Trancriptional activators, coactivators, and repressors

Transcriptional activator protein GAL4

Enhancers, silencers and insulators

Enhancer: DNA sequence stimulating transcription from a distance away from promoter

May increase transcription of many genes in vicinity

Silencer: Opposite of enhancer. Distant DNA sequence that binds a protein that inhibits transcription.

Insulator: DNA sequence that blocks or insulates the effect of enhancers

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

Gene regulation through RNA splicing

The degradation of RNA

5′-cap removal

Shortening of the poly(A) tail

Degradation of 5′ UTR, coding sequence, and 3′ UTR

Small interfering RNAs and microRNAs

RISC: RNA-induced silencing complex

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

Model Genetic Organism

The plant Arabidopsis thaliana