Molecular Biology of the Cell Sixth Edition

Home , Gene expression, Tryptophan repressor

Alberts • Johnson • Lewis • Morgan • Raff • Roberts • Walter Molecular Biology of the Cell Sixth Edition

Chapter 7 Control of Gene Expression

Su-May Yu

Totipotency was first described plants in 1953: The ability of a single cell to divide and produce all of the differentiated cells in an organism

Hormone adjustment

All genetic information are in the same nucleus. It is a matter how the genetic information becomes functional. The Different Cell Types of a Multicellular Organism Contain the Same DNA

Somatic cells

Embryonic cells

All genetic information are in the same nucleus. The Different Cell Types of a Multicellular Organism Contain the Same DNA

Somatic cells

Embryonic cells

All genetic information are in the same nucleus. RNA sequencing (RNAseq)

Isolation of mRNA Reverse transcription Different Cell Types Synthesize Different Sets of RNAs and Proteins

5’ UTR 5’ untranslated region mRNA

All genetic information are in the same nucleus. It is a matter how the genetic information becomes functional. Different Cell Types Synthesize Different Sets of RNAs and Proteins

Separated by pH Separated by molecular mass Isoelectric point (pI, pH(I), IEP), is the pH at which a - - particular molecule carries no net electrical charge

Protein + + Gene Expression Can Be Regulated at Many of the Steps in the Pathway from DNA to RNA to Protein The Sequence of Nucleotides in the DNA Double Helix Can Be Read by Proteins

Required for transcription of genetic information.

Major protein recognition site

Major protein recognition site Transcription Regulators Contain Structural Motifs That Can Read DNA Sequences

• TF recognizes specific sequences of DNA (typically 5-10 bp). • These DNA sequences are called cis-regulatory sequences/elements. • The interaction is highly specific and very strong. Transcription regulator or transcription factor (TF) Transcription Regulators Contain Structural Motifs That Can Read DNA Sequences

Dimers have a more strong binding affinity to DNA.

Major groove

Major groove Transcription Regulators Contain Structural Motifs That Can Read DNA Sequences

Help to position the recognition helix

Major groove Transcription Regulators Contain Structural Motifs That Can Read DNA Sequences

Major groove

Major groove Transcription Regulators Contain Structural Motifs That Can Read DNA Sequences TF may contain > 1 activation domain, but rarely > 1 DNA-binding domain. Dimerization of Transcription Regulators Increases Their Affinity and Specificity for DNA • Cis-regulatory sequences are read as double-stranded DNA, but only one strand is shown in a logo. • The same TF can be “reused” or becomes partner or other TFs.

homo homo

Three different DNA-binding specificities are formed from two transcription regulators. Regulation of Chromatin Structure

• Genes within highly packed heterochromatin are usually not expressed

• Chemical modifications to histones and DNA of chromatin influence both chromatin structure and gene expression

Polycistronic mRNA The Tryptophan Repressor Switches Genes Off An Activator and a Repressor Control the Lac Operon CAP Lac

• Lactose is a disaccharide sugar composed of galactose and glucose that is found in milk. • The gene product of lacZ is β-galactosidase

(activator)

Lac Z DNA Looping Can Occur During Bacterial Gene Regulation Organization of a Typical Eukaryotic Gene

TATA box – for positioning RNA polmerase II to initiate transcription

Enhancer Proximal Poly-A (distal control control Transcription signal Transcription elements) elements start site sequence termination region DNA Exon Intron Exon Intron Exon

Upstream Downstream Promoter Transcription Poly-A signal Primary RNA Exon Intron Exon Intron Exon Cleaved transcript 5′ 3′ end of (pre-mRNA) RNA processing primary transcript Intron RNA

Coding segment

mRNA G P P P AAA ⋅⋅⋅AAA 3′ Start Stop 5′ Cap 5′ UTR codon codon 3′ UTR Poly-A tail A Eukaryotic Gene Control Region Consists of a Promoter Plus Many cis-Regulatory Sequences Could be chromatin remodeling complex

Multi-protein co-activator

Figure 11-1 Overview of transcription control in multicellular eukaryotes. The Sequence of Nucleotides in the DNA Double Helix Can Be Read by Proteins

Histone acetyltransferase

Histone deacetylase

• Acetylation removes the positive charge on the histones.  decreases the interaction of the N termini of histones with the negatively charged phosphate groups of DNA.  The condensed chromatin is transformed into a more relaxed structure.  greater levels of gene transcription. Eukaryotic Transcription Activators Direct the Modification of Local Chromatin Structure

Ac Ac Ac Ac Eukaryotic Transcription Activators Direct the Modification of Local Chromatin Structure

Condensed

Chromatin is tightly condensed and in a transcriptionally silent form

-CH3 Figure 7-50d Molecular Biology of the Cell (© Garland Science 2008) Transcription Activators Work Synergistically Eukaryotic Transcription Repressors Can Inhibit Transcription in Several Ways Transcription Regulators Are Brought Into Play by Extracellular Signals The Drosophila Eve Gene Is Regulated by Combinatorial Controls Figure 18.11 Enhancer Promoter

Albumin gene

Crystallin gene The availability of transcription factors LIVER CELL LENS CELL NUCLEUS NUCLEUS determines the tissue- specific expression of Activators target genes. available

Activators unavailable

Albumin gene Albumin gene not expressed expressed Activators available

Activators unavailable

Crystallin gene not expressed Crystallin gene expressed (a) Liver cell (b) Lens cell