Tnlo-Encoded Tet Repressor Can Regulate an Operator-Containing
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Galactosidase
Copyright 0 1988 by the Genetics Society of America Effects of Amino Acid Substitutions atthe Active Site in Escherichia coli @-Galactosidase Claire G. Cupples and Jeffrey H. Miller Molecular Biology Institute and Department of Biology, University of Calqornia, Los Angeles, Calqornia 90024 Manuscript received April 2 1, 1988 Accepted July 23, 1988 ABSTRACT Forty-nine amino acid substitutions were made at four positions in the Escherichia coli enzyme p- galactosidase; three of the four targeted amino acids are thought to be part of the active site. Many of the substitutions were made by converting the appropriate codon in lacZ to an amber codon, and using one of 12 suppressor strains to introduce the replacement amino acid. Glu-461 and Tyr-503 were replaced, independently, with 13 amino acids. All 26 of the strains containing mutant enzymes are Lac-. Enzyme activity is reduced to less than 10% of wild type by substitutions at Glu-461 and to less than 1% of wild type by substitutions at Tyr-503. Many of the mutant enzymes have less than 0.1 % wild-type activity. His-464 and Met-3 were replaced with 1 1and 12 amino acids, respectively. Strains containing any one of these mutant proteins are Lac+. The results support previous evidence that Glu-46 1 and Tyr-503 areessential for catalysis, and suggest that His-464 is not part of the active site. Site-directed mutagenesis was facilitated by construction of an fl bacteriophage containing the complete lacz gene on i single ECORIfragment. -GALACTOSIDASE (EC 3.2.1.23) is produced in and J. -
Preinitiation Complex
Science Highlight – June 2011 Transcription Starts Here: Structural Models of a “Minimal” Preinitiation Complex RNA polymerase II (pol II) plays a central role in the regulation of gene expression. Pol II is the enzyme responsible for synthesizing all the messenger RNA (mRNA) and most of the small nuclear RNA (snRNA) in eukaryotes. One of the key questions for transcription is how pol II decides where to start on the genomic DNA to specifically and precisely turn on a gene. This is achieved during transcription initiation by concerted actions of the core enzyme pol II and a myriad of transcription factors including five general transcription factors, known as TFIIB, -D, -E, -F, -H, which together form a giant transcription preinitiation complex on a promoter prior to transcription. One of the most prominent core promoter DNA elements is the TATA box, usually directing transcription of tissue-specific genes. TATA-box binding protein (TBP), a key component of TFIID, recognizes the TATA DNA sequence. Based on the previous crystallographic studies, the TATA box DNA is bent by nearly 90 degree through the binding of TBP (1). This striking structural feature is thought to serve as a physical landmark for the location of active genes on the genome. In addition, the location of the TATA box at least in part determines the transcription start site (TSS) in most eukaryotes, including humans. The distance between the TATA box and the TSS is conserved at around 30 base pairs. TBP does not contact pol II directly and the TATA-containing promoter must be directed to the core enzyme through another essential transcription factor TFIIB. -
BMB400 Part Four - II = Chpt
BMB400 Part Four - II = Chpt. 17. Transcriptional regulation by effects on RNA polymerase B M B 400 Part Four: Gene Regulation Section II = Chapter 17. TRANSCRIPTIONAL REGULATION EXERTED BY EFFECTS ON RNA POLYMERASE [Dr. Tracy Nixon made major contributions to this chapter.] A. The multiple steps in initiation and elongation by RNA polymerase are targets for regulation. 1. RNA Polymerase has to * bind to promoters, * form an open complex, * initiate transcription, * escape from the promoter, * elongate , and * terminate transcription. See Fig. 4.2.1. 2. Summarizing a lot of work, we know that: • strong promoters have high KB, high kf, low kr, and high rates of promoter clearance. • weak promoters have low KB, low kf, high kr, and low rates of promoter clearance. • moderate promoters have one or more "weak" spots. 3. To learn these facts, we need: • genetic data to identify which macromolecules (DNA and proteins) interact in a specific regulation event, and to determine which base pairs and amino acid residues are needed for that regulation event. • biochemical data to describe the binding events and chemical reactions that are affected by the specific regulation event. Ideally, we would determine all forward and reverse rate constants, or equilibrium constants (which are a function of the ratio of rate constants) if rates are inaccessible. Although, in reality, we cannot get either rates or equilibrium constants for many of the steps, some of the steps are amenable to investigation and have proved to be quite informative about the mechanisms of regulation. BMB400 Part Four - II = Chpt. 17. Transcriptional regulation by effects on RNA polymerase Fig. -
Targets TFIID and TFIIA to Prevent Activated Transcription
Downloaded from genesdev.cshlp.org on September 26, 2021 - Published by Cold Spring Harbor Laboratory Press The mammalian transcriptional repressor RBP (CBF1) targets TFIID and TFIIA to prevent activated transcription Ivan Olave, Danny Reinberg,1 and Lynne D. Vales2 Department of Biochemistry and 1Howard Hughes Medical Institute, University of Medicine and Dentistry of New Jersey, Robert Wood Johnson Medical School, Piscataway, New Jersey 08854 USA RBP is a cellular protein that functions as a transcriptional repressor in mammalian cells. RBP has elicited great interest lately because of its established roles in regulating gene expression, in Drosophila and mouse development, and as a component of the Notch signal transduction pathway. This report focuses on the mechanism by which RBP represses transcription and thereby regulates expression of a relatively simple, but natural, promoter. The results show that, irrespective of the close proximity between RBP and other transcription factors bound to the promoter, RBP does not occlude binding by these other transcription factors. Instead, RBP interacts with two transcriptional coactivators: dTAFII110, a subunit of TFIID, and TFIIA to repress transcription. The domain of dTAFII110 targeted by RBP is the same domain that interacts with TFIIA, but is disparate from the domain that interacts with Sp1. Repression can be thwarted when stable transcription preinitiation complexes are formed before RBP addition, suggesting that RBP interaction with TFIIA and TFIID perturbs optimal interactions between these coactivators. Consistent with this, interaction between RBP and TFIIA precludes interaction with dTAFII110. This is the first report of a repressor specifically targeting these two coactivators to subvert activated transcription. [Key Words: RBP; transcriptional repression; TFIIA/TFIID targeting] Received November 17, 1997; revised version accepted April 1, 1998. -
Polycomb Repressor Complex 2 Function in Breast Cancer (Review)
INTERNATIONAL JOURNAL OF ONCOLOGY 57: 1085-1094, 2020 Polycomb repressor complex 2 function in breast cancer (Review) COURTNEY J. MARTIN and ROGER A. MOOREHEAD Department of Biomedical Sciences, Ontario Veterinary College, University of Guelph, Guelph, ON N1G2W1, Canada Received July 10, 2020; Accepted September 7, 2020 DOI: 10.3892/ijo.2020.5122 Abstract. Epigenetic modifications are important contributors 1. Introduction to the regulation of genes within the chromatin. The poly- comb repressive complex 2 (PRC2) is a multi‑subunit protein Epigenetic modifications, including DNA methylation complex that is involved in silencing gene expression through and histone modifications, play an important role in gene the trimethylation of lysine 27 at histone 3 (H3K27me3). The regulation. The dysregulation of these modifications can dysregulation of this modification has been associated with result in pathogenicity, including tumorigenicity. Research tumorigenicity through the increased repression of tumour has indicated an important influence of the trimethylation suppressor genes via condensing DNA to reduce access to the modification at lysine 27 on histone H3 (H3K27me3) within transcription start site (TSS) within tumor suppressor gene chromatin. This methylation is involved in the repression promoters. In the present review, the core proteins of PRC2, as of multiple genes within the genome by condensing DNA well as key accessory proteins, will be described. In addition, to reduce access to the transcription start site (TSS) within mechanisms controlling the recruitment of the PRC2 complex gene promoter sequences (1). The recruitment of H1.2, an H1 to H3K27 will be outlined. Finally, literature identifying the histone subtype, by the H3K27me3 modification has been a role of PRC2 in breast cancer proliferation, apoptosis and suggested as a mechanism for mediating this compaction (1). -
Molecular Biology and Applied Genetics
MOLECULAR BIOLOGY AND APPLIED GENETICS FOR Medical Laboratory Technology Students Upgraded Lecture Note Series Mohammed Awole Adem Jimma University MOLECULAR BIOLOGY AND APPLIED GENETICS For Medical Laboratory Technician Students Lecture Note Series Mohammed Awole Adem Upgraded - 2006 In collaboration with The Carter Center (EPHTI) and The Federal Democratic Republic of Ethiopia Ministry of Education and Ministry of Health Jimma University PREFACE The problem faced today in the learning and teaching of Applied Genetics and Molecular Biology for laboratory technologists in universities, colleges andhealth institutions primarily from the unavailability of textbooks that focus on the needs of Ethiopian students. This lecture note has been prepared with the primary aim of alleviating the problems encountered in the teaching of Medical Applied Genetics and Molecular Biology course and in minimizing discrepancies prevailing among the different teaching and training health institutions. It can also be used in teaching any introductory course on medical Applied Genetics and Molecular Biology and as a reference material. This lecture note is specifically designed for medical laboratory technologists, and includes only those areas of molecular cell biology and Applied Genetics relevant to degree-level understanding of modern laboratory technology. Since genetics is prerequisite course to molecular biology, the lecture note starts with Genetics i followed by Molecular Biology. It provides students with molecular background to enable them to understand and critically analyze recent advances in laboratory sciences. Finally, it contains a glossary, which summarizes important terminologies used in the text. Each chapter begins by specific learning objectives and at the end of each chapter review questions are also included. -
Solutions for Practice Problems for Molecular Biology, Session 5
Solutions to Practice Problems for Molecular Biology, Session 5: Gene Regulation and the Lac Operon Question 1 a) How does lactose (allolactose) promote transcription of LacZ? 1) Lactose binds to the polymerase and increases efficiency. 2) Lactose binds to a repressor protein, and alters its conformation to prevent it from binding to the DNA and interfering with the binding of RNA polymerase. 3) Lactose binds to an activator protein, which can then help the RNA polymerase bind to the promoter and begin transcription. 4) Lactose prevents premature termination of transcription by directly binding to and bending the DNA. Solution: 2) Lactose binds to a repressor protein, and alters its conformation to prevent it from binding to the DNA and interfering with the binding of RNA polymerase. b) What molecule is used to signal low glucose levels to the Lac operon regulatory system? 1) Cyclic AMP 2) Calcium 3) Lactose 4) Pyruvate Solution: 1) Cyclic AMP. Question 2 You design a summer class where you recreate experiments studying the lac operon in E. coli (see schematic below). In your experiments, the activity of the enzyme b-galactosidase (β -gal) is measured by including X-gal and IPTG in the growth media. X-gal is a lactose analog that turns blue when metabolisize by b-gal, but it does not induce the lac operon. IPTG is an inducer of the lac operon but is not metabolized by b-gal. I O lacZ Plac Binding site for CAP Pi Gene encoding β-gal Promoter for activator protein Repressor (I) a) Which of the following would you expect to bind to β-galactosidase? Circle all that apply. -
Mechanism of Promoter Repression by Lac Repressor–DNA Loops Nicole A
156–166 Nucleic Acids Research, 2013, Vol. 41, No. 1 Published online 9 November 2012 doi:10.1093/nar/gks1011 Mechanism of promoter repression by Lac repressor–DNA loops Nicole A. Becker1, Justin P. Peters1, Troy A. Lionberger2 and L. James Maher III1,* 1Department of Biochemistry and Molecular Biology, Mayo Clinic College of Medicine, 200 First Street Southwest, Rochester, MN 55905, USA and 2Howard Hughes Medical Institute and Jason L. Choy Laboratory of Single-Molecule Biophysics, Department of Physics, University of California, Berkeley, CA 94720, USA Received June 29, 2012; Revised October 1, 2012; Accepted October 2, 2012 ABSTRACT presence of allolactose or its analog, isopropyl b-D-1- thiogalactopyranoside (IPTG), relieving repression. In the The Escherichia coli lactose (lac) operon encodes absence of glucose, RNA polymerase binds cooperatively the first genetic switch to be discovered, and lac with catabolite activator protein at the lac promoter (positive remains a paradigm for studying negative and control). In simplest terms, the mechanism of negative positive control of gene expression. Negative control involves Lac repressor binding to occlude access control is believed to involve competition of RNA of RNA polymerase holoenzyme to the lac promoter (4). polymerase and Lac repressor for overlapping Of particular significance to the present work is the binding sites. Contributions to the local Lac repres- fascinating observation that two remote auxiliary oper- sor concentration come from free repressor and re- ators (Oaux) exist in the lac operon (5). It has been pressor delivered to the operator from remote proposed and demonstrated (6–13) that bidentate repres- auxiliary operators by DNA looping. -
Transcription in Eukaryotes
Transcription in eukaryotes Chromatin structure and its effects on transcription RNA polymerases Promoters General Transcription Factors Activators and Repressors Enhancers and ( Silencers ) Order of events leading to transcription initiation in eukaryotes at a specific promoter CRC … and chemical DNA modifications The order of steps on the pathway to transcription initiation appears to be different for different promoters Acção concertada de: -Activadores/ repressores ( proteínas auxiliares acessórias) -Proteínas de remodelação da cromatina -Capacidade de ligação dos factores gerais da transcrição Chromatin Remodeling Complexes (CRC) or Nucleosome remodeling factors ATPase/Helicase activity and DNA binding protein motifs Histone acetylation is one of the Histone histone chemical modifications acetylation characteristic of actively transcribed chromatin Interaction with other histones and with DNA Lys + HAT- histone acetyltransferase HDAC- histone deacetylase DNA chemical modifications affecting transcription initiation in eukaryotes How DNA methylation may help turning off genes? The binding of gene regulatory proteins and the general transcription machinery near an active promoter may prevent DNA methylation by excluding de novo methylases . If most of these proteins dissociate from the DNA, however, as generally occurs when a cell no longer produces the required activator proteins , the DNA becomes methylated , which enables other proteins to bind, and these shut down the gene completely by further altering chromatin structure . DNA -
Constitutive Expression KE YE, CHARLES A
Proc. Natl. Acad. Sci. USA Vol. 90, pp. 2295-2299, March 1993 Immunology Identification of the promoter region of human interleukin 1 type I receptor gene: Multiple initiation sites, high G+C content, and constitutive expression KE YE, CHARLES A. DINARELLO*, AND BURTON D. CLARK Department of Medicine, Tufts University School of Medicine and New England Medical Center, Boston, MA 02111 Communicated by Anthony S. Fauci, December 10, 1992 (receivedfor review November 10, 1992) ABSTRACT To better understand the role ofinterleukin 1 the regulation of expression of the IL-1RI gene at the (IL-1) and its receptor in disease, we have isolated a genomic molecular level, we cloned, identified, and characterized the clone of the human IL-1 type I receptor and have identified the 5' flanking region of this gene.t promoter region. There are multiple transcriptional initiation sites as demonstrated by primer extension. DNA sequence analysis shows that the promoter region contains neither a MATERIALS AND METHODS TATA nor a CAAT box; however, the 5' upstream regulatory Screening of Human Genomic Library. A human placental elements contain two AP-1-like binding sites. The internal genomic library was purchased from Clontech. This library regulatory sequences found immediately downstream to the 5' was prepared by partial Sau3A digestion and cloned into the transcriptional start site contain four Spl binding domains and BamHI site of EMBL-3 vector. Recombinant phage (106) have a high G+C content of 75%. This portion of the 5' were screened from the library through hybridization with a untranslated region of the mRNA can form stable secondary human IL-1RI cDNA probe (from position 1 to 959, a 5' Xba structure as predicted by computer modeling. -
Dynamics and Function of DNA Methylation in Plants
REVIEWS Dynamics and function of DNA methylation in plants Huiming Zhang1,2*, Zhaobo Lang1,2 and Jian- Kang Zhu 1,2,3* Abstract | DNA methylation is a conserved epigenetic modification that is important for gene regulation and genome stability. Aberrant patterns of DNA methylation can lead to plant developmental abnormalities. A specific DNA methylation state is an outcome of dynamic regulation by de novo methylation, maintenance of methylation and active demethylation, which are catalysed by various enzymes that are targeted by distinct regulatory pathways. In this Review, we discuss DNA methylation in plants, including methylating and demethylating enzymes and regulatory factors, and the coordination of methylation and demethylation activities by a so- called methylstat mechanism; the functions of DNA methylation in regulating transposon silencing, gene expression and chromosome interactions; the roles of DNA methylation in plant development; and the involvement of DNA methylation in plant responses to biotic and abiotic stress conditions. DNA methylation at the 5ʹ position of cytosine contrib- and regulatory factors are generally not lethal. However, utes to the epigenetic regulation of nuclear gene expres- DNA methylation appears to be more crucial for devel- sion and to genome stability1,2. Epigenetic changes, opment and environmental- stress responses in plants including DNA methylation, histone modifications and that have more complex genomes. Recent findings histone variants and some non- coding RNA (ncRNA) have uncovered important -
I = Chpt 15. Positive and Negative Transcriptional Control at Lac BMB
BMB 400 Part Four - I = Chpt 15. Positive and Negative Transcriptional Control at lac B M B 400 Part Four: Gene Regulation Section I = Chapter 15 POSITIVE AND NEGATIVE CONTROL SHOWN BY THE lac OPERON OF E. COLI A. Definitions and general comments 1. Operons An operon is a cluster of coordinately regulated genes. It includes structural genes (generally encoding enzymes), regulatory genes (encoding, e.g. activators or repressors) and regulatory sites (such as promoters and operators). 2. Negative versus positive control a. The type of control is defined by the response of the operon when no regulatory protein is present. b. In the case of negative control, the genes in the operon are expressed unless they are switched off by a repressor protein. Thus the operon will be turned on constitutively (the genes will be expressed) when the repressor in inactivated. c. In the case of positive control, the genes are expressed only when an active regulator protein, e.g. an activator, is present. Thus the operon will be turned off when the positive regulatory protein is absent or inactivated. Table 4.1.1. Positive vs. negative control BMB 400 Part Four - I = Chpt 15. Positive and Negative Transcriptional Control at lac 3. Catabolic versus biosynthetic operons a. Catabolic pathways catalyze the breakdown of nutrients (the substrate for the pathway) to generate energy, or more precisely ATP, the energy currency of the cell. In the absence of the substrate, there is no reason for the catabolic enzymes to be present, and the operon encoding them is repressed. In the presence of the substrate, when the enzymes are needed, the operon is induced or de-repressed.