Lecture Connections 28 | Regulation of Gene Expression

Lecture Connections 28 | Regulation of Gene Expression © 2009 W H Freeman and Company CHAPTER 28 Regulation of Gene Expression Key topics: – DNA elements that control transcription – Protein factors that control transcription – Lac operon as a model for regulation – Regulation of protein synthesis by RNA How to Control Protein’s Activity in The Cell? • How much primary RNA transcript to make? • How to process this RNA into mRNA? • How rapidly to degrade the mRNA? • How much protein to make from this mRNA? • How efficiently to target the protein to its location? • How to alter the intrinsic activity of this protein? • How rapidly to degrade the protein? Processes that Affect Protein’s Concentration and Activity DNA Sequences Involved in Regulation of Gene Expression • Most bacterial promoters include the conserved –10 and –35 regions that interact with the  factor of RNA polymerase • Some promoters also include the upstream element that interacts with the  subunit of RNA polymerase Two Main Mechanisms to Regulate Transcription in Bacteria • Use of different  factors – These recognize different classes of promoters – Allows coordinated expression of different sets of genes • Binding other proteins (transcription factors) to promoters – These recognize promoters of specific genes – These may bind small signaling molecules – These may undergo post-translational modifications – The protein’s affinity toward DNA is altered by ligand binding or post-translational modifications – Allows expression of a specific genes in response to signals in the environment Regulation by  Factors Regulation of Transcription in Eukaryotes • General transcription factors – TATA box binding protein (TBP) – Transcription factors for the assembly of the initiation complex • Promoter proximal / distal enhancer binding factors – Homeodomain proteins share similarities with helix-turn-helix bacterial counterparts nut often involve water bridges between DNA and protein – Leucine zippers are made of two amphipathic polypeptides One side of each peptide is hydrophobic, facilitating dimerization – Zinc fingers form elongated loops held together by a single Zn++ ion Homeodomain Proteins • Notice that an -helix interacts with DNA via the major groove Leucine Zippers Eukaryotic Promoters and Regulatory Proteins Activation of Bacterial Translation by small RNA Molecules • The ribosome-binding Shine-Dalgarno sequence is sequestered into a stem-loop structure in the mRNA • In the presence of protein Hfq, small regulatory RNA DsrA binds to the mRNA • The binding of DsrA opens up the stem-loop and allows mRNA binding to ribosome • DsrA RNA promotes translation Inhibition of Bacterial Translation by small RNA Molecules • The ribosome-binding Shine-Dalgarno sequence is sequestered into a stem-loop structure in the mRNA • In the presence of protein Hfq, small regulatory RNA OxyS binds to the mRNA • The binding of OxyS blocks the ribosome binding site in mRNA • OxyS RNA inhibits translation Chapter 28: Summary In this chapter, we learned that: • Regulation of gene transcription is a common and efficient way to control protein’s activity in the cell • Regulation of transcription is commonly achieved via binding of inhibiting and activating proteins to the DNA near the beginning of the gene • Transcription factors frequently bind via an  helix that protrudes into the major groove of dsDNA • Binding of mRNA to ribosome is modulated by small regulatory RNA molecules ...CHAPTER 28 Regulation of Gene Expression Key topics: – DNA elements that control transcription – Protein factors that control transcription – Lac operon as a model for regulation – Regulation of protein... classes of promoters – Allows coordinated expression of different sets of genes • Binding other proteins (transcription factors) to promoters – These recognize promoters of specific genes – These... post-translational modifications – Allows expression of a specific genes in response to signals in the environment Regulation by  Factors Regulation by Transcription Factors (1) Regulation by Transcription