8: Viral DNA replication Flashcards
Which classes need viral DNA replication
- ssDNA: parvovirus
- dsDNA: adenovirus, HSV, papilloma
- Delayed after infection
- One protein to be synthesize
Rules for viral DNA replication
- DNA is synthesized by incorporation of dNMPS into 3-OH of DNA chain
- Synthesized 5-3’
- Replication starts at ORI
- Catalyzed by host/viral DdDp
- Primer-dependent (RNA/DNA/protein) or primer independent
Where does DNA polymerase come from? How does polymerase build DNA?
-small genome: don’t encode for DdDp, use host DNA pol
eg. papillo, polyo, parvo
- large genome: encode for their own replication system (herpes,adeno,pox)
Its builds DNA by two-metal (Mg) mechanism and two aspartic acid residues:
1.ion deprotonates 3’ OH group
- ion releases pyrophosphate (ppi)
What proteins does viral DNA replication require?
- At least one viral protein
eg. polymerase, helicase, ligase, exonuclease, - Viruses with small genomes use host proteins
- Viruses with larger genomes encode their own proteins
What are the two mechanisms for viral DNA synthesis?
- Replication Fork (RNA primer)
- papilloma, polyoma, herpes, retro
- Strand replacement (Protein/DNA primer)
- adenovirus, parvovirus, poxvirus
After DNA synthesis RNA primers are removed and gaps are present at the end of the DNA strands
SV40 (polyoma)
- dscircular, ORI, bidirectional with replication fork (semi discontinuous)
- presence of ATP, 6 large T bind sites around ORI, (protects AT and EP from DNase 1)
- LT conformational changes to EP, unwind ORI (help = RP-A, Topo 1)
- Polα- primase binds RP-A + LT -> RNA primer +DNA fragment ->
RF-C + Pcna binds. -> Polα leaves and Polε binds (leading strand) - lagging strand: RNA primer/short DNA, Polδ synth, primers removed by RNAase H and exonuclease. gaps repaired by Polδ and DNA ligase
Parvovirus (AAV2)
ssDNA, DNA hairpin (ITR) acts as a DNA primer
Strand displacement
Continuous replication
- Elongation dsDNA
- Rep 78/68 nicks for new 3’-OH
- Elongation from nick, copies 5’ ITR seq
- Ds replication seq.
- Hairpins reform
- displacement
- Repeats
Adenovirus (Protein Priming)
(dsDNA, strand displacement, ORI + Terminal Protein)
- Pre initiation complex (viral pTP and DNA pol)
- Builds 3 bases, uses primer to displace (DBP coats)
- ITR to pTP-pol to cycle (cleave pTP = mature)
HSV
2 OriS and 1OriL
(Host proteins Circularization)
- Replicates as a rolling circle (replication fork)
- Nick one strand
- Produces concatemers (long-multiple copies of genomes)
Poxvirus (DNA priming)
- Strand displacement
- DNA primer
- Cytoplasm (encodes all proteins)
- Viral ori : AT-rich + binding sites
- RT: Termin (integration) and Baltimore
