Chapter 8 - Temperate Bacteriophage

Chapter 8 - Temperate Bacteriophage - Lysogeny:the paradigm...

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 Lysogeny: the λ  paradigm
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Typical  fried egg  appearance of  wild-type  φλ  plaques ( TURBID  PLAQUES ) M13 T3 Plaques
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New concepts 1.  Regulation of gene expression by transcription  antitermination. 2.  Lysogeny 3.  Site-specific recombination 4.  Immunity to superinfection 5.  Phage induction by DNA damage 6.  Prophage-associated bacterial pathogenicity factors and  chromosomal pathogenicity islands Phage   and Lysogeny λ
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CI Cro "Lysogenic" cell  proliferation Int/Xis Integration CI, Int Ghost (RecA + DNA  damage) Phage  λ   life styles  and some  enabling  gene  products See also  Fig. 8.1
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Fig 8.2 Genetic map of phage  λ λ :  linear form in phage head
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Genetic Map of Linear phage   DNA: this form is  λ packaged in phage head Fig. 8.2 cos att ori Head Recombination Tail Early regulation Immunity DNA replication Late gene  regulation Lysis P R M P R Left and right  cos  sites (cohesive ends) are short complementary single-stranded  sequences that base pair for circularization of injected DNA. LATE GENES
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Circular  λ  DNA formed by base pairing and ligation of  cos  ends  of the linear DNA after injection into host cells Fig 8.3 cos Terminase Ligase The  λ  cos site
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Some important    λ proteins and sites 3 4
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Fig 8.3 Lytic development: Stages of gene expression First, genes  N  and  cro  are  transcribed from  p R  and  p L  and translated. Next, genes for  replication  and  recombination are  transcribed and  translated. Finally, “late” genes,  encoding phage structural  components and lysis are transcribed  and translated. N cro O P exo bet gam R S A B C D E F G H M L K I J cos Q
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Phage    λ early, middle and late gene transcription DNA R1 R2 R3 R4 R5 t att   int  xis  red  nut    p N p cI  nut    t cro cII OP  t t    p'   qut  t Q Late genes  L1 L2 NOTES 1.  Protein N  acts at  nutL  and  nutR  sites. 2.  Protein Q  acts at  qut  site. 3.  Notice similarity to    ρ and  rut  sites, except that  ρ  effects  termination rather than antitermination. Antitermination by N and Q N Q
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Fig 8.4 R 1 Antitermination by  N
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Antitermination N  binds to  nut   in the RNA and the RNA  polymerase as the latter transcribes a  nut   sequence.  Association of  N  with the  RNA Pol results in transcription through  t R 1 Without  N t R 1 With N and NusABEG t R 1 A B E G A B E G N
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The sites include SIMILAR  box A box B , and sometimes  box C   sequences. The potential  RNA-hairpin structure  of  box B  is critical for  antitermination function.
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Chapter 8 - Temperate Bacteriophage - Lysogeny:the paradigm...

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