Lecture 3.10 Notes

Lecture 3.10 Notes - Notes Gene Exchange in Prokaryotes Transformation free DNA taken up and incorporated Transduction virus-mediated transfer of

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Notes – 3/10/10 Gene Exchange in Prokaryotes Transformation –free DNA taken up and incorporated Transduction – virus-mediated transfer of genes Conjugation – DNA exchange via cell-cell contact and a conjugative plasmid Molecular events of homologous recombination All Bacteria , Archaea and Eukarya contain genes homologous to E coli recA , which encodes a DNA binding protein that promotes the process of homologous recombination. RecA initiates a multistep pathway that can have a variety of outcomes but all share the feature of promoting exchange between two homologous regions of different DNA molecules. Process: Endonuclease nicks DNA Nicked strand displaced by protein w/ helicase activity, which can sometimes be the nuclease itself such as the E. coli RecBCD nuclease. Binding of single strand binding protein and RecA facilitates annealing with complementary strand in adjacent DNA duplex (strand invasion) Pairing of DNA molecules over long stretches leads to heteroduplex regions Resolution of products by DNA nucleases and ligases. For new genotypes to emerge from recombination, the 2 homologous sequences must be genetically distinct Eukaryotes are diploid and always contain genetically distinct homologues (i.e., maternal and paternal chromosomes) Prokaryotes are haploid but can have recombination between fragments of a donor chromosome and a recipient via horizontal gene transfer by transformation, transduction and conjugation. Detection of recombination Usually relies on recipient lacking a selectable marker that is gained by recombination. For powerful selection, reversion rate of marker must be low More selective power by use of double mutants Transformation First demonstration by Griffith and Avery Some species of bacteria transformable, others not Competence in naturally transformable bacteria is regulated Competence-specific proteins:
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Membrane-associated DNA binding protein Cell wall autolysin Various nucleases Natural competence in
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Lecture 3.10 Notes - Notes Gene Exchange in Prokaryotes Transformation free DNA taken up and incorporated Transduction virus-mediated transfer of

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