Lecture.18.Fall.2013 - Viral Genetics Gene Regulation in...

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Viral Genetics (Chapter 8) – Bacteriophage (phage) – Transduction (generalized and specialized) – Mapping genes using generalized transduction Gene regulation (Chapter 16) Elements common to bacteria and eukaryotes Genes and regulatory elements Levels of gene regulation DNA-binding proteins Viral Genetics Gene Regulation in Bacteria October 30, 2013
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Viral Genetics Gene Regulation in Bacteria October 30, 2013 Gene regulation in prokaryotes Operons The lac and trp operons Catabolite repression
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Techniques for the study of bacteriophage Bacteriophage must be cultured in bacterial cells Phage are mixed with bacteria and plated on solid medium on a petri plate. A high concentration of bacteria is used so that the colonies fuse, forming a “lawn”.
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Techniques for the study of bacteriophage A single phage infects a single bacterium. When it lyses, the adjacent bacteria are infected, and so on. This results in a clear patch of lysed cells called a plaque . Number of plaques = number of phage in original solution.
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Transduction Three mechanisms of bacterial gene transfer: Conjugation Transformation Transduction: genes are transferred between bacteria by viruses
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Transduction Two types of transduction: Specialized transduction: Only a few genes can be transferred.
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Not all phage are capable of transduction. It requires: 1. A phage infection that leads to degradation of the bacterial chromosome 2. That the process of viral DNA packaging not be specific for phage DNA Generalized transduction
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3. That bacterial genes transferred recombine with the chromosome on the recipient cell Transduction rate is typically low (1/100,000 to 1/1,000,000) Generalized transduction
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Generalized transduction can be used to map genes
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Specialized transduction and bacteriophage λ (lambda) λ is a temperate phage - it can undergo lysogeny It integrates into the host genome, then excises when it enters the lytic cycle This can result in the simultaneous excision of host genes that get packaged into the phage.
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Specialized transduction and bacteriophage λ (lambda) Similar to F’ cells, in which the F plasmid carries genes from one bacterium into another
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Alfred Hershey and Raquel Rotman Rotman (in Hershey’s lab) discovered that phage genes have a linear map that can be deduced by recombination frequencies This finding opened the way for: the molecular biological reform of genetics Seymour Benzer’s frameshift experiments to determine the molecular nature of the gene and, ultimately, the genetic code. ~ “We Can Sleep Later”, Edited by Franklin W. Stahl CSHL Press
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Looked at two loci in T2 phage: h + : able to infect and lyse type B, but not type B/2 E. coli cells.
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