Polyomavirus (Dr. Frappier) Flashcards
Features of capsid of polyomaviruses
nonenveloped icosahedral
features of genome for genome
circular, dsDNA with histons
How is genome organized?
early region and late region separated by regulatory region
what is found in regulatory region?
origin of DNA replication, promoter, enhancer
What is found in late region?
structural proteins like 3 capsid proteins (VP1, VP2, VP3)
What is found in early regions?
T antigens (types depending on specific polyomaviruses)
Difference in early region of SV40 and polyoma
i) SV40 don’t have tiny and middle T
ii) Polyoma have all tiny, small, middle and large T antigens
What is used for transcription of polyomavirus?
cellular RNA polymerase II
What does middle T antigen do?
i) bind PP2A (phosphatase) and SRC kinase to affect their activity
–> SRC kinase activated – phosphorylate T and other cellular protein
Needed for cell transformation
similarities between small t and large T
their N-terminal region
Special about small t of SV40
C terminal can bind and inhibit PP2A
–> contribute to cell transformation
Main functions of large T antigen
i) stimulate resting cells to enter cell cycle
ii) regulates early mRNA production
iii) needed for viral DNA replication
How does large T antigen stimulate resting cells to enter cell cycle?
i) bind pRb
ii) bind p53 (only for SV40 T)
iii) interact with p300/CBP
iv) bind hsp70
How does binding to pRB stimulate resting cells to enter cell cycle?
pRb released from E2F
–> activate genes involved in cell proliferation by E2F
What kind of infection occur in primate of polyoma?
non permissive
How does binding to p53 stimulate resting cells to enter cell cycle?
i) inhibit p54 binding to DNA
–> lower expression of cell cycle inhibitors
ii) inhibit p53 mediated apoptosis
How does binding to p300 stimulate resting cells to enter cell cycle?
changes the histone acetylation and expression of specific genes (e.g. E1A)
How does binding to hsp70 stimulate resting cells to enter cell cycle?
i) stimulate ATPase activity of hsp70
ii) N terminal domain of T binding to hsp70
–> important for cell trnasformation
Name for N terminal domain of large T
DnaJ
How does large T antigen regulate early mRNA production?
Bind site I in regulatory region
–> interferes with RNA pol and TFs binding to early promoter
–> repress early gene expression at end of early phase
How does large T antigen required for viral DNA replication?
i) bind origin to initiate DNA replication
ii) melt origin DNA and serve as DNA helicase
iii) bind cellular DNA replication proteins
How many origin of replication is found in SV40?
one
What is found within the origin of replication?
core + auxiliary sequences
Features of SV40 core sequence
i) T binding site II
ii) palindrome on early side
iii) AT-rich on late side
Features of SV40 auxiliary sequences
i) transcriptional elements
ii) T binding sites I
What kind of infection occur in primate of SV40?
permissive
What kind of infection occur in rodent of SV40?
nonpermissive
How does DNA replication start in SV40?
i) T forms 2 hexamers on site II of origin
ii) T unwinds at early palindrome
–> RPA bind ssDNA
iii) T recruits polymerase alpha primase to origin to initiate DNA synthesis
iv) T hexamer at each end act as DNA helicase
What mechanism does SV40 replication operate on?
theta structure mechanism
Cellular proteins needed for SV40 replication
i) RPA (bind ssDNA)
ii) DNA polymerase alpha primase (initiate replication on both strands)
iii) DNA polymerase delta (make leading strand, extend lagging strand)
iv) PCNA
v) RFC (load PCNA on DNA)
vi) Topoisomerase I, II (relieves strained bits)
vII) RNaseI, FEN-1 (Exonuclease to remove RNA primters)
viii) DNA ligase
Where does permissive infection occur for each virus?
SV40 –> primate
Polyoma –> rodent
Where does nonpermissive infection occur for each virus
SV40 –> rodent
Polyoma –> primate
What kind of infection occur in rodent of polyoma?
permissive
Difference between permissive and nonpermissive infection
i) virions formed in permissive infection, not formed in nonpermissive
ii) viral DNA replicates in permissive, not in nonpermissive
types of nonpermissive infection
i) transient transformation
ii) Permanent transformation
Difference between transient and permanent transfomraiton
i) T antigen expression: lack in transient, continued in permanent
Which T antigen is expressed during permanent transformation?
SV40: largeT
polyoma: middle T
T antigens expressed by merkel cell polyomavirus
small t
large T
57 kT
ALTO
contributing factors to merkel cell carcinoma
i) UV exposure
ii) immunosuppresion
lethality of merkel cell carcinoma compared to malignant melanoma
twice as lethal as merkel cell carcinoma
What is found in tumor cells of merkel cell carinoma?
integrated copies of merkel cell polyomavirus
function of small T in merkel cell polyomavirus
protects large T from degradation by inhibiting ubiquitin ligase
Difference between largeT found in normal cells and tumor cells
tumor cells
–> truncated
–> N terminal here but lack DNA helicase domain
What is important for transformation in merkel cell polyomavirus?
large T binding to Rb
What is found in tumor in raccons?
cirular form of polyomavirus
–> nonintegrated
