Papoviridae Flashcards
____ is an oncogenic DNA virus
Simian Virus 40
- induces primary brain and bone cancers, malignant mesothelioma, lymphomas in lab animals
- epidemiological evidence shows that SV40 likely does not cause cancer in humans
SV40 genome
- early region: expressed prior to onset of viral DNA replication, encodes viral tumor antigens (T antigens)
- late region: encodes viral capsid proteins
Roles of viral T antigens
- alter and/or recruit specific host cell proteins to participate in virus production
- block cellular antiviral defense systems
- participate directly in viral replication
Large T antigens are _____ and are required to _______
DNA helicases; replicate viral DNA
3 mRNA expressed by SV40
- large T antigen
- small t antigen
- tiny t antigen
All T antigens encoded by a virus have a common _______
Amino-terminal domain
Only _____ and _____ are essential for productive infection and viral tumorigenicity
Large T antigen (SV40) and large/middle T antigens (PyV)
Small t antigens contribute to _______
Both infection and transformation
Budgerigar fledgling disease virus
Isolated from papillomas on legs of European finches and in proliferative lesions on the head and eyelids of African grey parrots
- murine polyomavirus
- has oncogenic potential
Does BFD infect Budgies?
No, but can infect other species (adults are carriers)
- in baby budgies it causes generalized infection –> lack of down feathers, retarded growth of tail and feathers, distended abdomen
- dehydration leads to a reddish skin coloration
Post mortem examination of BFD
- hydropericardium
- cardiomegaly
- hepatic necrosis
- enlarged hyperemic kidneys
- karyomegalic inclusions on histopath
Morphology
Nonenveloped, isometric nucleocapsids (round)
- 40-44 nm in diameter
- icosahedral symmetry
- incomplete viral particles present as empty capsids
Nucleic acid
10-13% nucleic acid content in virions, with one molecule of circular dsDNA
Human papillomaviruses all target _______
Epithelial tissues for infection
- productive life cycle is linked to epithelial differentiation
Papillomaviruses establish their genomes as _______
Multicopy nuclear episomes
- viral DNA is replicated with cellular chromosomes
- daughter cell migrates away from basal layer to undergo differentiation
What property allows papillomavirus to persist for several decades, or until the immune system clears the infection?
Virion production is limited to differentiated cells
____ and ____ genes encode for oncoproteins
E6 and E7
- target Rb and p53
- facilitate stable maintenance of episomes and stimulate differentiated cells to reenter S phase
Papillomavirus morphology
Non-enveloped
- virions are of one type of particle only, or more than one type of particle
- icosahedral symmetry
Papillomavirus genome
One molecule of circular, dsDNA
Why are papillomaviruses good models for studying molecular evolution of DNA?
Large number of isolates are available that exhibit genomic diversity and host species and tissue specificity
- phylogeny suggests that some branches of papillomavirus evolution are restricted to particular target tissues = long-term papillomavirus-host coevolution has occurred
What is the first virus isolated from the order Sirenia?
Trichechus manatus latirostris
- novel papillomavirus found in Florida manatee
- was one of the first wart viruses to evolve
