Prof. Gerald Cohen

מקרוביולוגיה מולקולרית אמריטוס
Prof. Gerald Cohen
Phone: 03-6409649



1961 Helen Hay Whitney Postdoctoral Fellow, NIH, Bethesda, MD, USA
1968 Ph.D; Weizmann Institute, Rehovot, Israel
1961 B.Sc.; University College, London England


Academic Positions:

1995- present Professor; Dept. Mol. Microbiology and Biotechnology, TAU
1985-1995 Associate Professor; Dept of Mol. Microbiology & Biotechnology, TAU
1975-1985  Senior Lecturer; Dept Microbiology and Immunology, TAU
1971-1975 Lecturer; Dept. Microbiology and Immunology, TAU

Honorary Appointments and Administrative Activities:

2002 - present  President of the Society of the Genetics of Industrial Microorganisms GIM,  
1997 - present  Director; Joan and Jaime Constantiner Institute of Molecular Genetics, Tel Aviv University 
1998 Co-organizer; 8th International Symposium on the Genetics of Industrial Microorganisms, GIM
1993-1997 Editorial Board; Trends in Biotechnology
  Section Editor; ASM Manual of Industrial Microbiology


Research Grants:

2001-2004 The Israel Science Foundation:  Regulation of the Staphylococcus aureus ribonucleotide reductase genes at the aerobic-anaerobic interface
1997- 2000, 2000- 2003 The Israel Science Foundation:  Mechanism of Action of Isopenicillin N Synthase
1995- 1998 German-Israel Binational Science Foundation:  
Management of Oxidative Stress in the Listerial Host Cell Interaction
1994-1997 US-Binational Science Foundation: Structure Function of Isopenicillin N Synthase


Research Interests

My research interests are:

  • Thiol-disulfide redox metabolism in Streptomyces
  • Regulation of gene expression in Staphylococcus aureus in response to oxygen
  • Ribonucleotide reductases in Gm+ bacteria
  • Structure-function of isopenicillin N synthase
  • Drug targeting, Antibacterials


Major Research Activities:

  1. Microbial Thiol-Disulfide Redox Metabolism:  Enzymatic thiol-disulfide exchange reactions play a key role in many metabolic processes. Our interest focuses on the nature and activity of such redox systems in the biology of gram-positive bacteria that lack glutathione, in particular in their growth and development, for the production of secondary metabolites and as targets for creating new antibacterial drugs. We have shown that Streptomyces and Mycobacterium and many other members of the high G+C branch of the acti nomycetes contain an unusual low molecular weight thiol, termed mycothiol (MSH), that is present in millimolar intracellular concentrations. MSH may play an analogous role to that of glutathione - once thought to be ubiquitous in living organisms - in maintaining the reducing thiol-disulfide status of the cytoplasm, as a hydrogen donor for essential cellular processes, and in the elimination of reactive oxygen species (33,38, 41). In Streptomyces and in some other gram-positive bacteria, including Staphylococcus aureus the major thiol-disulfide reductase is thioredoxin/thioredoxin reductase (32,34). We are currently examining the regulation of the thiol redox systems in these bacteria in response to disulfide stress (51) and to other environmental stress agents as well as their potential as targets for the development of new classes of antibacterial drugs (47).
  2. Genetic and Biochemical Studies of Ribonucleotide Reductase:  Ribonucleotide reductases (RNR) are essential enzymes that catalyze the reduction of ribonucleotides to deoxyribonucleotides for DNA replication and repair. We have cloned and sequenced the Streptomyces nrdAB and nrdJ genes encoding class Ia oxygen-dependent and class II oxygen-independent ribonucleotide reductases and shown that they are differentially transcribed during vegetative growth (49). Studies are directed towards determining the cellular roles of the two RNRs. Similar studies with Staphylococcus aureus reveal that they contain genes coding for class Ib aerobic and class III anaerobic ribonucleotide reductases that are regulated in response to changes in oxygen tension (50). We are currently investigating the molecular mechanisms that control the expression of these genes in anaerobiosis.
  3. Structure-Function Studies of Isopenicillin N Synthase:  Isopenicillin N synthase is a non-heme ferrous iron dependent dioxygenase that plays a central role in penicillin biosynthesis, catalyzing a unique reaction in which a linear tripeptide, delta-(L-alpha-aminoadipoyl)-L-cysteinyl-D-valine (ACV), is oxidized to form a bicyclic beta-lactam antibiotic (56). Our studies are directed towards elucidating the nature of the substrate binding and catalytic active-site domains, thereby enabling a better understanding of the reaction mechanism. Site-directed mutagenesis and sequence analysis were used to identify the endogenous active-site ligands and led to the assignment of a novel motif for iron binding (40, 43, 46). The crystal structure of the Streptomyces jumonjinensis IPNS and of a substrate-inhibitor complex were recently determined and afford new insights into the mechanism of the cyclization reaction.
  4. Crystal structure of Streptomyces IPNS


Recent Publications

Refereed articles

G. O'Reagan, N. Sternberg and G. Cohen. "Construction of an ordered overlapping library of bacteriophage P1 DNA in phage vector lambda D69".Gene, 60, (1987), 129-135. medline


C. Keen, S. Mendelovitz, G. Cohen, Y. Aharonowitz and K. Roy. "Isolation and characterization of a linear DNA plasmid from Streptomyces clavuligerus".Mol. Gen. Genet., 212, (1988), 172-176. medline


D. Shiffman, M. Mevarech, G. Cohen, S. Jensen and Y. Aharonowitz. "Cloning and comparative sequence analysis of the gene coding for isopenicillin N synthase in Streptomyces". Molec. Gen. Genet., 214, (1988), 562-573. medline


G. Cohen and N. Sternberg."Genetic analysis of the lytic replicon of bacteriophage P1. I. Isolation and partial characterization". J. Mol. Biol., 206, (1989), 99-109. medline


N. Sternberg and G. Cohen. "Genetic analysis of the lytic replicon of bacteriophage P1. II. Organization of replicon elements". J. Mol. Biol., 206, (1989), 111-133. medline


D. Shiffman, G. Cohen, Y. Aharonowitz, H. Palissa, H. von Dohren, H. Kleinkauf and M. Mevarech. "Isopenicillin N synthase gene of the unicellular gram-negative Flavobacterium." Nucleic Acid. Res., 18, (1990), 660. medline


G. Cohen, D. Shiffman, M. Mevarech and Y. Aharonowitz. "Microbial isopenicillin N synthases: structure, function, diversity and evolution".Trends in Biotechnology, 8, (1990), 105-111.medline


G. Landan, G. Cohen, Y. Aharonowitz, Y. Shuali, D. Graur and D. Shiffman. "Evolution of the microbial isopenicillin N synthase genes probably involved horizontal gene transfer".Mol. Biol. Evol., 7, (1990), 399-406. medline


O. Landman, D. Shiffman, Y. Av-Gay, Y. Aharonowitz and G. Cohen."High level expression in Escherichia coli of isopenicillin N synthase gene from Flavobacterium and Streptomyces and recovery of active enzyme from inclusion bodies." Fems Microbiol. Lett., 84, (1991), 239-244. medline


Y. Av-Gay, Y. Aharonowitz and G. Cohen."Streptomyces contain a 7.0 kDa cold shock like protein." Nucleic Acid Res., 20, (1992). medline


Y. Aharonowitz, G. Cohen and J.F. Martin,"Penicillin and cephalosporin biosynthetic genes: structure, organization, regulation and evolution." Ann. Rev. Microbiol., 46, (1992), 461-495. medline

Y. Aharonowitz, Y. Av-Gay, R. Schreiber and G. Cohen. "Characterization of a thioredoxin-like disulfide reductase from Streptomyces clavuligerus and its possible role in ß-lactam biosynthesis." J. Bacteriology, 175, (1993), 623-629. medline
G. Newton, R. Fahey, G. Cohen and Y. Aharonowitz. "Low molecular weight thiols in streptomycetes and their potential role as antioxidants." J. Bacteriology, 175, (1993), 2734-2742. medline
G. Cohen, M. Yanko, M. Mislovati, A. Argaman, R. Schreiber, Y. Av-Gay and Y. Aharonowitz. "Thioredoxin-thioredoxin reductase system of Streptomyces clavuligerus: sequences, expression and organization of genes."
J. Bacteriology, 175, (1993), 5159-5167.  medline
Y. Aharonowitz, J. Bergmeyer, J. Cantoral, G. Cohen, A. Demain, U. Fink, H. Kinghorn, H. Kleinkauf, A. MacCabe, H. Palissa, E. Pfeifer, T. Schwecke, H. van Liempt, H. von Dohren, S. Wolfe and J. Zhang. "ACV synthetase, the multienzyme integrating the four primary reactions in beta-lactam biosynthesis, as model peptide synthetase." Bio/Technology, 11, (1993), 807-810. medline
G. Cohen, A. Argaman, R. Schreiber, M. Mislovati and Y. Aharonowitz. "Thioredoxin system of Penicillium chrysogenum and its possible role in penicillin biosynthesis." J. Bacteriology, 176, (1994), 973-984. medline
I. Sanyal, G. Cohen and D. Flint. "Biotin synthase: Purification, characterization as a [2Fe-2S] cluster protein, and in vitro activity of the Escherichia colibioB gene product." Biochemistry, 33, (1994), 3625-3631. medline
G. Newton, C. Bewley, T. Dwyer, R. Horn, Y. Aharonowitz, G. Cohen, J. Davies, D. Faulkner and R. Fahey. "The structure of U17 isolated from Streptomyces clavuligerus and its properties as an antioxidant thiol." Eur. J. Biochemistry, 230, (1995), 821-825. medline
K. Gibson, G. Lorimer, A. Rendina, W. Taylor, B. Wexler, G. Cohen, A. Gatenby, W. Payne, D. Roe, B. Lockett, E. Marsilii, I. Turner, C. Kalba and H. Chi."Dethiobiotin synthetase: the carbonylation of 7,8-diaminononanoic acid proceeds regiospecifically via the N7-carbamate". Biochemistry, 34, (1995), 10976-10984. medline
I. Borovok, O. Landman, R. Kreisberg, Y. Aharonowitz and G. Cohen. "The ferrous active site of isopenicillin N synthase: genetic and sequence analysis of the endogenous ligands."
Biochemistry 35, (1996), 1881-1887. medline
Newton, K. Arnold, M. Price, C. Sherill, S. Delcardayre, Y. Aharonowitz, G. Cohen, J. Davies, R. Fahey and C. Davis. "Distribution of thiols in microorganisms: mycothiol is a major thiol in most actinomycetes". J. Bacteriology. 178, (1996), 1990-1995. medline
G. Cohen, E. Or, W. Minas and N. Sternberg. "Directionality of bacteriophage P1 replication and role of cis-acting elements". Gene. 175 (1996), 151-155.  medline
O. Landman, I. Borovok, Y. Aharonowitz and G. Cohen. "The glutamine ligand in the ferrous active-site of isopenicillin N synthase of Streptomyces jumonjinensis is not essential for catalysis". FEBS Letters 405 (1997), 172-174.  medline
S. Liu, S. Sela, G. Cohen, J. Jadoun, A. Cheung and I. Ofek. "Genetic evidence for co-regulation of Streptolysin S production and riboflavin biosynthesis in Streptococcus pyogenes". Microbial Pathogenesis. 22 (1997) 227-234. medline
O. Gal-Mor, I. Borovok, Y. Av-Guy, G. Cohen and Y. Aharonowitz. "Gene organization in the trxA/B - oriC region of the Streptomyces coelicolor chromosome and comparison with other eubacteria".Gene. 217 (1998), 83-90. medline
R. Kreisberg-Zakarin, I. Borovok, M. Yanko, F.Frolow, Y. Aharonowitz and G. Cohen.
"Structure function studies of the non - heme iron active site of isopenicillin N synthase: some implications for catalysis". Biophysical Chemistry (2000), 86, 109-118. medline
G. Cohen, I. Borovok, O. Uziel, R. Schreiber and Y. Aharonowitz. "Bacterial thiol-disulfide redox metabolism: A new target for rational drug design". Periodicum Biologorum (2001), 103, 153-155. medline
D. Govorko, G. Cohen and B. Solomon "Single-chain antibody against the common epitope of mutant p53: isolation and intracytosolic expression in mammalian cells." Journal of Immunological Methods (2001), 258, 169-181. medline
I. Borovok, R. Kreisberg-Zakarin, M. Yanko, R. Schreiber, M. Myslovati, F. Aslund, A. Holmgren, G. Cohen and Y. Aharonowitz. "Streptomyces contain class Ia and class II ribonucleotide reductases: expression analysis of the genes in vegetative growth."
Microbiology (in press).
M. Masalha, I. Borovok, R. Schreiber, Y. Aharonowitz and G. Cohen. "Transcriptional Analysis of the Staphylococcus aureus Aerobic Class Ib and Anaerobic Class III Ribonucleotide Reductase Genes in Response to Oxygen." J. Bacteriology (2001), 183, 7260-7272 medline
M. Paget, V. Molle, G. Cohen,Y. Aharonowitz and M. Buttner. "Defining the disulfide stress response in Streptomyces coelicolor A3(2): identification of the oR regulon." Molecular Microbiology (2001), 42, 1007-1002 medline
Chapters in Books
Y. Aharonowitz and G. Cohen. "Bioactive secondary metabolites." In: Biotechnology: Potentials and Limitations. Ed. S. Silver and P. Abelson. Report of Dahlem Workshop, pp. 99-112, Berlin, Springer Verlag, Berlin, (1985).
G. Cohen and Y. Aharonowitz. "Molecular genetics of antimicrobials: A case study of beta-lactam antibiotics." In: The Society of General Microbiology Symposium, Fifty Years of Antimicrobials, pp. 139-163, Cambridge University Press, (1995).
A. Gargir, S. Liu, S. Sela, G. Cohen, J. Jadown, A. Cheung and I. Ofek. "Biological significance of the genetic linkage between streptolysin S expression and riboflavin biosynthesis inStreptococccus pyogenes". Adv. Exp. Med. Biol. 418, (1997) 987-989.
G. Cohen. "Introduction to the Genetics of Industrial Microorganisms". In: Manual of Industrial Microbiology and Biotechnology, 2nd edition (Eds. A.Demain and J. Davies), American Society for Microbiology, ASM Press, Washington DC.
R. Kreisberg-Zakarin, I. Borovok, M. Yanko, Y. Aharonowitz and G. Cohen. "Recent advances in the structure and function of isopenicillin N synthase" In: Antonie van Leeuwenhoek: Biosynthesis of beta -lactam antibiotics. 75 (1999), pp 33-39, Kluwer Academic Publishers, The Netherlands.
Y.Aharonowitz, L. Van der Voort, G. Cohen, R. Bovenberg, R. Schreiber, A. Argaman, Y. Av-Gay, H. Nan, A. Kattevilder, H. Palissa and H. Van Liempt.  "An oxido reductase enzyme system obtainable from P. chrysogenum, the set of genes encoding the same and the use of oxido reductase enzyme systems or genes encoding the same for increasing antibiotic production".  
European Patent Application No. 91201542.7
Publication No. EP 0-462-674-A1.
Date of filing 18.06.91.
Y.Aharonowitz, L. van der Woort, G. Cohen, R. Bovenberg, R. Schreiber, A. Argaman, Y. Av-Gay, H. Nan, A. Kattevilder, H. Palissa and H. van Liempt. "Oxido reductase enzyme system obtained from P. chrysogenum.
U.S. Patent No. 5,328,839
Date of Patent: 12.07.94.
O.Uziel, I. Borovok, G. Cohen and Y. Aharonowitz. "Recombinant Staphylococcus aureus thioredoxin reductase, the use of the enzyme system or genes encoding the same as targets for new antimicrobial drugs development and its inhibitors as antimicrobial agents".
U.S. Patent Application pending.
D.Govorko, G. Cohen and B. Solomon. "Construction of a single chain antibody (scFv) against the conserved epitope of mutant p53 protein in human tumors and its application for cancer therapy".
U.S. Patent Application pending.
Tel Aviv University, P.O. Box 39040, Tel Aviv 6997801, Israel
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