BBlecture10S09s - gex1 Principles of Bacterial Genetics...

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Unformatted text preview: gex1 Principles of Bacterial Genetics Principles (genetic exchange in prokaryotes) 11.9: 11.9: 11.10: 11.11: 11.11: 11.12: 11.12: 11.13: Genetic Recombination Genetic Transformation Transduction Transduction Conjugation: Essential Features The Formation of Hfr Strains and The Chromosome Mobilization Chromosome 11.14: Complementation 11.15: Gene Transfer in Archaea 11.16: Mobile DNA: Transposable Elements genetic recombination: genetic • SSB – single stranded binding protein • RecA-like proteins found in all prokaryotes, yeast, higher eukaroytes examined gex2 • resolution involves nuclease and DNA ligase activities (Fig 11.13, 12th ed) A B gex2a fret not; for illustration only! a A b B A B chi form a isomerize b resolution A B A b a resolution b b patch a a B exchange of flanking markers (splices) DNA transfer: DNA gex3 transduction: transfer of host genes from one host to another by a virus (Fig 11.12, 12th ed) transformation: transfer of bacterial genes involving free DNA conjugation: transfer of genes from one prokaryotic cell to another by mechanism involving cell-to-cell contact and a plasmid search for a rare genetic recombinant amongst nonrecombinants is based on selectable markers: nonrecombinants gex4 (Fig 11.14, 12th ed) Griffith’s experiment with pneumococcus (now Streptococcus pneumoniae): Streptococcus gex5 (Fig 11.15, 12th ed) S: “smooth” colony morphology (encapsulated) R: “rough” colony morphology (no capsule) transformation: transformation • requires competent cells (or electroporation) gex6 (Fig 11.16, 12th ed) generalized transduction: generalized • host DNA derived from virtually any part of host genome can be involved gex7 (Fig 11.17, 12th ed) specialized transduction: transduction • DNA involved is from a specific region of host genome only gex8 (Fig 11.18, 12th ed) genetic map of the F plasmid: genetic genes involved in conjugative transfer gex9 (Fig 11.19, 12th ed) transfer of plasmid DNA by conjugation: conjugation gex10 (Fig 11.21(a), 12th ed) contact between two conjugating bacteria: contact gex10a + fimbriae F cell (Fig 11.20, 12th ed) • initiated via pilus • retraction of pilus within donor cell draws two cells together • transfer of DNA occurs once mating pair drawn together replication and transfer process: replication gex11 (Fig 11.21(b), 12th ed) integration of F plasmid into chromosome: integration gex12 Hfr cells: high frequency of recombination • cells with chromosomeintegrated F plasmid (Fig 11.22, 12th ed) • breakage of Hfr chromosome at OriT • beginning of transfer to F- recipient gex13 (Fig 11.23, 12th ed) transfer of chromosomal DNA by conjugation: transfer gex14 recombination of donor DNA into recipient chromosome (Fig 11.24, 12th ed) different Hfr strains: different • circular bacterial chromosome can open at various insertion sequences at which the F plasmids become inserted gex15 (Fig 11.25, 12th ed) Joshua Lederberg Joshua Lederberg & Tatum (1946) • do bacteria have sex? gex15a • “plasmid” to describe apparently extrachromosomal genetic elements (1950s) Zinder & Lederberg (1952) • transduction Nobel Prize (1958) for work in bacterial genetics 2005 - Lederberg still conducted lab research on bacterial & human genetics; advised government & industry on global health policy, biological warfare, & threat of bioterrorism (Profiles in Science: http://profiles.nlm.nih.gov/BB/ ) • procedure to detect genetic conjugation: procedure gex16 (Fig 11.26, 12th ed) gex17 rate of recombinant formation after mixing Hfr & F- bacteria: rate (Fig 11.27, 12th ed) gex18 complementation analysis: analysis • both gene A & gene B products required for Trp+ phenotype (Fig 11.28, 12th ed) gene transfer in Archaea: gene • limited knowledge - practical problems! • extreme incubation conditions may be required • unaffected by many “usual” antibiotics → limited availability of selectable markers for genetic crosses • isn’t one model organism → scattered work & knowledge (extreme halophiles, methanogens) • examples of transformation, viral transduction, conjugation known • mechanism(s) of conjugation probably differ from what is seen in Bacteria • several plasmids been isolated gex19 maps of transposable elements: maps gex20 (Fig 11.30, 12th ed) gex21 the transposition process: the • note origin of duplicated target sequence (Fig 11.31, 12th ed) mechanisms of transposition: mechanisms gex22 (Fig 11.32, 12th ed) transposon mutagenesis: transposon gex23 (Fig 11.33, 12th ed) ...
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