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Viral DNA replicationLecture 8
Biology 3310/4310 Virology
Spring 2018
The more the merrier --ANONYMOUS
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Influenza virus
Reovirus Rotavirus
Hepatitis B virus
Parvovirus
RetrovirusAdenovirus Herpes simplex virus Polyoma- and Papillomaviruses
Poliovirus
©Principles of Virology, ASM Press
VII
Virology Lectures 2018 • Prof. Vincent Racaniello • Columbia University
Viral DNA genomes must be replicated to make new progeny
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Base
5’-3’-
OH-3’OH
P
-5’Primer
Direction Of Chain Growth
Universal rules of DNA replication
• DNA is synthesized by template-directed incorporation of dNMPs into 3’-OH of DNA chain
• DNA is always synthesized 5’-3’ via semiconservative replication (two daughter strands)
• Replication initiates at specific sites on template called origins
• Catalyzed by DdDp + accessory proteins
• Always primer-dependentVirology Lectures 2018 • Prof. Vincent Racaniello • Columbia University
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Base
5’-3’-
OH-3’OH
P
-5’Primer
Direction Of Chain Growth
©Principles of Virology, ASM PressVirology Lectures 2018 • Prof. Vincent Racaniello • Columbia University
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What’s the host for? Viruses can’t do it themselves
• Viral DNA replication always requires synthesis of at least one viral protein, sometimes many (hence always delayed after infection)
• Simple viruses require more host proteins - genetic economy
• Complex viruses encode many, but not all proteins required for replication
©Principles of Virology, ASM PressVirology Lectures 2018 • Prof. Vincent Racaniello • Columbia University
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Where does the polymerase come from?
• Small DNA viruses do not encode an entire replication system
- Encode proteins that orchestrate the host
- Papillomaviridae, Polyomaviridae, Parvoviridae
• Large DNA viruses encode most of their own replication systems
- Herpesviridae, Adenoviridae, Poxviridae
©Principles of Virology, ASM PressVirology Lectures 2018 • Prof. Vincent Racaniello • Columbia University
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Viral proteins involved in DNA replication
• DNA polymerase and accessory proteins
• Origin binding protein, helicases
• Exonucleases
• Enzymes of nucleic acid metabolism (thymidine kinase, ribonucleotide reductase, dUTPase)
Virology Lectures 2018 • Prof. Vincent Racaniello • Columbia University
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1
Which statement about viral DNA synthesis is NOT correct?
A. Large DNA viruses encode many proteins involved in DNA synthesis B. Small DNA viruses encode at least one protein involved in DNA synthesis C. Viral DNA replication is always delayed after infection because it requires the
synthesis of at least one viral protein D. Some viruses encode all proteins needed for DNA replication
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Diverse structures of viral DNAs
©Principles of Virology, ASM PressVirology Lectures 2018 • Prof. Vincent Racaniello • Columbia University
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Two mechanisms of dsDNA synthesis
RNA primers Never RNA primed
©Principles of Virology, ASM PressVirology Lectures 2018 • Prof. Vincent Racaniello • Columbia University
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The 5’-end problem
Virology Lectures 2018 • Prof. Vincent Racaniello • Columbia University
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Lessons from SV40
©Principles of Virology, ASM Press
~5 kbp
Virology Lectures 2018 • Prof. Vincent Racaniello • Columbia University
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Semi-discontinuous DNA synthesis from a bidirectional origin
©Principles of Virology, ASM Press
No end problem!Virology Lectures 2018 • Prof. Vincent Racaniello • Columbia University
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Recognition and unwinding of SV40 origin
T has 3’-5’ helicase activity
©Principles of Virology, ASM Press
Rp-A binds LT!
Virology Lectures 2018 • Prof. Vincent Racaniello • Columbia University
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Synthesis of leading and lagging strands
Synthesis of RNA primers Synthesis of short DNA fragments
Synthesis of long DNA
Rf-C binds 3’OH along with PCNA and pol δ —RF-C a clamp loading protein —Allows entry of PCNA on DNA —Causes release of pol α Form sliding clamps along DNA
©Principles of Virology, ASM Press
Primase binds Rp-A and LT
Virology Lectures 2018 • Prof. Vincent Racaniello • Columbia University
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Synthesis of leading and lagging strands
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Function of topoisomerases
©Principles of Virology, ASM PressVirology Lectures 2018 • Prof. Vincent Racaniello • Columbia University
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2
The SV40 genome is a circular dsDNA. Which statement about its replication is correct?
A. Viral T antigen binds and unwinds the ori B. Replication is bidirectional from a single ori C. The 5’-end problem is solved D. Has leading and lagging strand synthesis E. All of the above
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DNA priming: Parvoviruses
ori
©Principles of Virology, ASM PressVirology Lectures 2018 • Prof. Vincent Racaniello • Columbia University
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• Replication is continuous
• No pol α, uses ITR to self-prime
• Requires pol δ, RF-C and PCNA
• Rep78/68 proteins are required for initiation and resolution: endonuclease, helicase, binds 5’-terminus
• No replication fork, strand displacement
©Principles of Virology, ASM Press
No end problem!
Virology Lectures 2018 • Prof. Vincent Racaniello • Columbia University
DNA priming: Parvoviruses
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Protein priming: Adenovirus
• Origins at both ends
• Strand displacement synthesis
• Semiconservative DNA replication©Principles of Virology, ASM PressVirology Lectures 2018 • Prof. Vincent Racaniello • Columbia University
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Protein priming: Adenovirus
Ad DNA pol links α-phosphoryl of dCMP to OH of Ser residue only when pTP is assembled with DNA pol into preinitiation complex at ori
ITRs
No end problem!
©Principles of Virology, ASM PressVirology Lectures 2018 • Prof. Vincent Racaniello • Columbia University
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Adenoviral ssDNA binding protein
©Principles of Virology, ASM PressVirology Lectures 2018 • Prof. Vincent Racaniello • Columbia University
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How is DNA replication of parvovirus and adenovirus similar?
A. They both require protein-linked primers B. Replication occurs by strand displacement C. DNA synthesis occurs in the cytoplasm D. A replication fork occurs in both E. None of the above
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Herpes simplex virus
• 2 oriS and a unique oriL sequence
• DNA enters as a linear molecule and converts to circle
• Replicates as rolling circle
• UL5, 8 and 53 - primase • UL42 - processivity protein • UL9 - origin binding protein • UL29 - ssDNA binding protein • UL30 - DNA polymerase
©Principles of Virology, ASM PressVirology Lectures 2018 • Prof. Vincent Racaniello • Columbia University
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Initiation of herpesvirus DNA replication
Host proteins are responsible for circularization
DNA ligase IV/XRCC4
©Principles of Virology, ASM PressVirology Lectures 2018 • Prof. Vincent Racaniello • Columbia University
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Rolling circle replication
©Principles of Virology, ASM Press
No end problem!
Virology Lectures 2018 • Prof. Vincent Racaniello • Columbia University
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Poxvirus
• All viruses discussed replicate in nucleus
• Poxviruses replicate in cytoplasm
©Principles of Virology, ASM PressVirology Lectures 2018 • Prof. Vincent Racaniello • Columbia University
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Poxvirus DNA factories
DNA DNA binding protein merge
Virology Lectures 2018 • Prof. Vincent Racaniello • Columbia University
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At least 15 viral proteins involved in viral DNA synthesis
Poxvirus DNA replication
©Principles of Virology, ASM Press
No end problem!
Virology Lectures 2018 • Prof. Vincent Racaniello • Columbia University
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4
What makes poxvirus DNA replication different from all of the other viruses we discussed today?
A. The complete replication machinery is encoded by the viral genome B. DNA synthesis occurs in the nucleus C. DNA synthesis occurs by strand displacement D. None of the above
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Viral origins
• AT-rich segments recognized by viral origin recognition proteins
• Assembly points for multi-protein DNA replication machines
• Some viral genomes have one ori; others up to 3
Ori
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Viral origins of DNA replication
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Viral origin recognition proteins
• Polyomavirus T binds specifically to DNA
• Papillomavirus E1 binds ori in presence of E2
• Parvovirus Rep68/78 binds at ends and unwinds DNA, also involved in terminal resolution
• Adenovirus pTP binds at terminus and recruits DNA pol
• Herpesvirus UL9 protein recruits viral proteins to AT-rich ori and then unwinds DNA
Virology Lectures 2018 • Prof. Vincent Racaniello • Columbia University
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SV40 large T
• T is a species-specific DBP/OBP
- Pre-initiation complexes do not form in the wrong species
- Failure to interact with DNA pol α - primase
• Binds and sequesters cell cycle regulators
- Causes cells to enter S phase©Principles of Virology, ASM PressVirology Lectures 2018 • Prof. Vincent Racaniello • Columbia University
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Regulation of DNA synthesis
• Most of our cells do not divide or do so rarely
• Viruses do not replicate well in quiescent cells
• Viruses must induce host replication proteins
• Done by virus encoded early gene products
Virology Lectures 2018 • Prof. Vincent Racaniello • Columbia University
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• Cellular retinoblastoma (rb) gene
• Rb protein controls entry into S
• Rb loss associated with tumors = tumor suppressor gene
Rb protein
Replication of DNA
©Principles of Virology, ASM PressVirology Lectures 2018 • Prof. Vincent Racaniello • Columbia University
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Abrogation of Rb by viral proteins
(needed for DNA synthesis, and to pass through cell cycle)
©Principles of Virology, ASM PressVirology Lectures 2018 • Prof. Vincent Racaniello • Columbia University