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TRANSDUCTION. Dr. W. McLaughlin. Transduction. Discovered in 1953 – Zinder & Lederberg Phage of S. enterica serovar typhimurium In transduction, DNA is transferred from cell to cell via virus mediated genetic transfer. Genetic transfer of host genes by viruses . Generalised transduction

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transduction

TRANSDUCTION

Dr. W. McLaughlin

transduction1
Transduction
  • Discovered in 1953 – Zinder & Lederberg
  • Phage of S. enterica serovar typhimurium
  • In transduction, DNA is transferred from cell to cell via virus mediated genetic transfer
genetic transfer of host genes by viruses
Genetic transfer of host genes by viruses
  • Generalised transduction
  • Specialised transduction
generalized transduction
Generalized transduction
  • Host DNA derived from virtually any portion of the host genome becomes part of the mature virus particle in place of the virus genome.
specialized transduction
Specialized transduction
  • DNA from a specific region of the host chromosome is integrated directly into the virus genome-usually replacing some of the virus genes.
  • Only bacterial genes close to the attachment site of the prophage can be integrated into the viral genome usually replacing some of the virus gene
  • This occurs in only some temperate viruses
transduction in bacteria
Transduction in bacteria
  • Desulfovibrio
  • E. coli
  • Psuedomonas
  • Rhodococcus
  • Rhodobacter
  • Salmonella
  • Staphylococcus
  • Xanthobacter
  • Methanobacterium thermoautotrophicum (Archea)
virus viability needs
Virus viability needs:
  • att (attachment site)
  • cos (cohesive sites for packaging)
  • ori (replication origin)
generalized transduction1
Generalized Transduction
  • Salmonella typhimurium with phage P22
  • The enzymes responsible for packaging viral DNA into the bacteriophage may sometimes accidentally package host DNA
  • Transducing particles are made when cleavages are made in the bacterial DNA at a site that closely resemble pac (packaging) site to allow the phage encoded endonuclease to act
generalized transduction2
Generalized Transduction
  • Host genes derived from any part of the host genome become part of the mature virus particle
  • The resulting particle is called a transducing particle
generalised transduction
Generalised transduction
  • On lysis of the cell, the transducing particles are released with the normal virions
  •  Transducing phages are normally defective as a virus because the bacterial genes have replaced the viral DNA. 
  • The defective phage DNA cannot replicate, but can undergo genetic recombination with the new host. If it does not, then it will be lost
specialized transduction1
Specialized Transduction
  • Results in the exchange of only a limited number of specific genes
  • A new virion having gained certain genes from the bacterial chromosome and have lost others from is own genome
  • Mediated in lysogenic E. coli cells only by temperatephages e.g .  phage
transducing phage
Transducing phage
  • Formed as a result of a mistake during the excision recombination of prophages
  • Phage excises incorrectly
integration
Integration
  • In a  lysogen of E. coil, the  prophage is integrated close to or between the galand bio genes in the chromosome
  • Viral DNA replication is now under control of the host
  • Most of the phage functions are repressed in the prophage
  • cI gene is expressed
induction
Induction
  • On induction (e.g. by UV radiation) of the prophage, the viral genome separates from the host DNA by a process that is the reverse of integration
  • a phage picks up neighbouring bacterial genes during induction of the prophage. e.g. gal or bio
transducing phage1
Transducing phage
  • dgal is defective because of the phage genes lost and does not make mature phage
  • dgal lacks essential head and tail genes and cannot multiply without a wild type  helper phage
  • pbio, the int and xis genes have been replaced by bio
transduction2
Transduction
  • If the transducing phage has been grown on a bacterial strain genetically different from the strain subsequently infected with the phage, genetically altered bacterium may be produced
  • If a gal- bacteria culture is infected with a dgal transducing phage then the gal genes can transduce the bacteria to gal+
generalised specialised transduction
Generalised & Specialised transduction
  • In specialised transduction this must occur by the induction of a lysogen
  • Generalised transduction can occur by induction of a lysogen or by infection of a non-lysogenic cell by a phage with subsequent replication and lysis
references
References
  • Lewin B. Genes VII Oxford University Press
  • Madigan M. T. Martinko J. M. and J. Parker Biology of Microorganisms 9th Edition. Prentice Hall
  • Brooker R. T. Genetics: Analysis and Principles. Addison Wesley Longman, Inc
  • Snyder L. and W. Champness Molecular Genetics of Bacteria 2nd Edition. ASM Press
  • Burton Z. F. and J. M. Kaguni Experiments in Molecular Biology: Biochemical Applications. Academic Press
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