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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