1 / 22

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

reyna
Télécharger la présentation

TRANSDUCTION

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  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

More Related