Sinh học - Chapter 21 (part 2): Transcriptional regulation and rna processing

Chapter 21 (Part 2)Transcriptional Regulation and RNA ProcessingRegulation of Gene ExpressionAAAAAA5’CAPmRNARNA ProcessingRNA DegradationProtein DegradationPost-translational modificationActiveenzymeActivators and RepressorsRNAPRNAPAco-Aco-R+1+1RThe Helix-Turn-Helix Motif contain two alpha helices separated by a loop with a beta turn The C-terminal helix fits in major groove of DNA; N-terminal helix stabilizes by hydrophobic interactions with C-terminal helix The Zn-Finger Motif Zn fingers form a folded beta strand and an alpha helix that fits into the DNA major groove. The Leucine Zipper Motif Forms amphipathic alpha helix and a coiled-coil dimer Leucine zipper proteins dimerize, either as homo- or hetero-dimers The basic region is the DNA-recognition site Basic region is often modeled as a pair of helices that can wrap around the major grooveTranscription Regulation in ProkaryotesBinding of some trans-factors is regulated by allosteric modificationlac operonGlucose is E. coli’s primary carbon source. But.. it can grow on different carbon sources. Diauxic growth of E. coli on a mixture of lactose + glucose.The lac I proteinOperator and RNA Polymerase Bind at Overlapping SitesInhibition of repression of lac operon by inducer binding to lacIInducer : Allolactose, produced by side reaction of lacZ Lehninger: Principles of Biochemistry, 3rd Ed.IPTG is a Gratuitous InducerSynthetic moleculeRepression of the Tryptophan operon:A variation of the themeCatabolite Repression of lac Operon (Positive regulation)Molecular Cell Biology, 4th Edition, Lodish et. al. (2000)Why does the Lac Operon need an activator?Lac promoter has lousy promoter!!!tRNA ProcessingrRNA ProcessingProcessing of Eukaryotic mRNASplicing of Pre-mRNA Splicing of Pre-mRNA