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Gene regulation allows for adaptation to environmental changes for an individual organism in the present. Pre-2001 (HGP). Epigenetic changes allows for adaptation to current environmental changes for an individual organism to be passed on to its offspring,

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  1. Gene regulation allows for adaptation to environmental changes for an individual organism in the present. Pre-2001 (HGP) Epigenetic changes allows for adaptation to current environmental changes for an individual organism to be passed on to its offspring, without changes in the DNA sequence 22%

  2. 50,000 bp ds DNA 15 coat proteins  Phage Infects E. coli

  3. Phage binds to Cell membrane.... ...... and inserts dsDNA into cell In the lytic phase the cell replicates the phage DNA New phage particles are created …. Then the cell is lysed and the virus is released to the environment to seek new hosts. E Coli cell

  4. Add phage – plaque forms With bacterial growth Petri Dish with Nutrients

  5. DNA inserted into bacterial chromosome Lysogenic Phase Dormant phage’s DNA Copied with each bacterial cell division cycle. E Coli cell

  6. Petri Dish plaques E. Coli cells (lysogenic) reclaim plaque areas, but give ‘turbid’ appearance. DNA damage can be induced by UV light and causes switch from lysogenic to lytic phase. Lysogenic E Coli cells are immune to l phage infection.

  7. phage infects E coli Cell very early phase (N/cro) Lytic early phase (cII/cIII) yes no Is host well fed? yes Lysogenic no Is host DNA Damaged? (UV) Dormancy

  8. |=10=cIII=N=OL=cI=OR=cro=cII=2=Q=3=|=12=10| cos attahed to host chromosome in host unattached in virus particle |=12=10|=10=cIII=N=OL=cI=OR=cro=cII=2=Q=3=| att

  9. PL PRE |=10=cIII=N= OL=cI=OR=cro=cII=2=Q=3=|=12=10| cos PRM PR PI PI 10: = 8 == Int == Xis == Lysogenic phase 2 = Replication genes 3 = Lysis genes 12 = Tail Protein genes 10 = Head Protein genes Lytic Phase

  10. REGULATORY GENES cI: ( Repressor) & Activator (favors lysogenic phase) cII: Activator (favors cI production over cro & Int) cro: activator & repressor (favors lytic phase) cIII: protects cII from proteases N & Q: antiterminators – bypass transcription stop signal PL PRE |=10=cIII=N= OL=cI=OR=cro=cII=2=Q=3=|=12=10| cos PRM PR PI

  11. cro- cro+- cII+ cI+- cI- PI PL PRMPRPRE PR’ PI PL PRMPRPRE PR’ LYS = cIII = N = OL = cI = OR = cro = cII = Q=Lyt LYS = cIII = N = OL = cI = OR = cro = cII = Q=Lyt lysogenic lytic

  12. phage infects E coli Cell very early phase (N/cro) Lytic early phase (cII/cIII) yes no Is host well fed? ↓[bacetrial protease] allows cIII time to protect cII. cI eventually dominates cro, and Int production. Int inserts phage DNA into host chromosome. Lysogenic ↑[bacetrial protease] destroys cII and cro dominance over cI is maintained. Dormancy

  13. PI PL PRMPRPRE PR’ LYS = cIII = N = OL = cI = OR = cro = cII = Q=Lyt OR1 OR3 OR2 <<< PRM PR >>>

  14. DNA double helix B Form minor groove major groove

  15. N N N N CH3 N N O N O H Major Groove A H H T Minor Groove

  16. CH2 CH2 O=C N N N N CH3 N H H N N O N O H Gln H H T

  17. -Turn HTH Motif R R Hydrophobic Contact R H-bonds to Major Groove

  18. Lambda Phage Repressor Protein

  19.  OR1 OR3 OR2 <<< PRM PR >>> cro cI dimer cro dimer 1st on 2nd on OR1 1 1 OR2 1 1 OR3 10 (10) 1st on 2nd on OR1 10 --- OR2 1 5 OR3 1 1

  20. RNA Pol cro OR1 OR3 OR2 <<< PRM PR >>> |=10=cIII=N=cI=OR=cro=cII=2=Q=3=|=12=10| cos 1st on 2nd on OR1 1 1 OR2 1 1 OR3 10 (10) cro is expressed, cI is repressed.

  21. cro cro cro OR1 OR3 OR2 <<< PRM PR >>> |=10=cIII=N=cI=OR=cro=cII=2=Q=3=|=12=10| cos High [cro] represses both PRM & PR

  22. RNA Pol OR1 OR3 OR2  PRM PR -repressor binding blocks PR … and activates  PRM 1st on 2nd on OR1 10 --- OR2 1 5 OR3 1 1  

  23. OR1 OR3 OR2 <<< PRM PR >>> |=10=cIII=N=cI=OR=cro=cII=2=Q=3=|=12=10| cos High [cI] represses PR & PRM   

  24. phage infects E coli Cell very early phase (N/cro) Lytic early phase (cII/cIII) [cI] remains high. Phage remains dormant. cI inhibits growth of any late-coming phage. Yes – bacterial SOS response genes activated Lysogenic no Is host DNA Damaged? (UV) Dormancy

  25. HTH E coli SOS Response E coli contains 17 SOS genes — e.g. HSPs encode DNA repair/recombination genes — LexA & RecA LexA Repressor of SOS operon LexA contains HTH motif & similar AG sequence to cI

  26. RecA Function Low [ ] under ‘normal’ circumstances binds to ssDNA: complex cleaves LexAat AG [RecA] - ssDNA + ATP  dsDNA + ADP If l phage lysogen then RecA cleaves cI and induces lytic phase shift

  27. phage infects E coli Cell very early phase (N/cro) Lytic early phase (cII/cIII) ↑RecA-ssDNA destroys cI, and [cro] recovers dominance over cI. Xis expression removes phage DNA from host chromosome. Lytic phase commences. [cI] remains high. Phage remains dormant. cI inhibits growth of any late-coming phage. yes Lysogenic no Is host DNA Damaged? (UV) Dormancy

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