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TRANSDUCTION

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

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  1. TRANSDUCTION Dr. W. McLaughlin

  2. 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

  3. Genetic transfer of host genes by viruses • Generalised transduction • Specialised transduction

  4. 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.

  5. 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

  6. Transduction in bacteria • Desulfovibrio • E. coli • Psuedomonas • Rhodococcus • Rhodobacter • Salmonella • Staphylococcus • Xanthobacter • Methanobacterium thermoautotrophicum (Archea)

  7. Virus viability needs: • att (attachment site) • cos (cohesive sites for packaging) • ori (replication origin)

  8. 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

  9. 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

  10. 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

  11. 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

  12. Transducing phage • Formed as a result of a mistake during the excision recombination of prophages • Phage excises incorrectly

  13. 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

  14. 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

  15. 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

  16. 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+

  17. 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

  18. 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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