Virology Tutorial Worksheet #2 Yellow fever virus is a virus that belongs to the genus Flavivirus. It is transmitted to people primarily through the bite of infected mosquitoes. Mosquitoes acquire the virus by feeding on infected primates (human or non-human) and then can transmit the virus to other primates (human or non-human). The majority of people infected with yellow fever virus will either not have symptoms, or have mild symptoms (fever/chills, body aches, nausea/vomiting) and completely recover. For people who develop symptoms, the time from infection until illness is typically 3 to 6 days. About 1 in 7 infected persons will develop severe disease which would include high fever, jaundice, bleeding, shock and organ failure (and possibly death). There is no medicine to treat or cure infection from yellow fever. People with severe symptoms of yellow fever infection should be hospitalized for close observation and supportive care. Because there is a risk of severe disease, all people traveling to an area at risk for the virus should be vaccinated before starting their travels. The virus is an enveloped particle about 40 - 60 nm in diameter. The genome is a single strand of RNA, approximately 10 kb in length. The virus has a single envelope protein called "E". The virus's replication cycle is shown below. 1 ENTRY VIA CLATHRIN- COATED PIT RECEPTOR BINDING BY VIRAL E GLYCOPROTEIN 4 Genomic RNA 2 3 5 Polyprotein CLEAVAGE BY HOST AND VIRAL PROTEINASES ACIDIFICATION, REARRANGEMENT OF E GLYCOPROTEIN TO FUSOGENIC FORM 6 Proteins 1 Antisense genomic RNA RF/RI Genomic RNA 10x excess 0 RNA replication at membranes in P INTRACELLULAR BUDDING ASSEMBLY 7 8 nes in perinuclear region C RF/RI - replicative form / replicative intermediate VACUOLAR TRANSPORT RELEASE HOST PROTEINASE CLEAVAGE OF VIRAL PRM GLYCOPROTEIN
1. The virus' genome must encode all of the proteins that it requires for replication of the virus. The flavivirus' genome codes for 3 or 4 protein products. List the genes that you would expect to find it is genome to code for the protein products. 2. The virus particle binds to a cell surface structure (1) and enters the cell in an endosome (it would remain attached to the cell surface structure. The endosome is then acidified (2). Look at the cartoon - what do you think it means by rearrangement of E glycoprotein to fusogenic form? 3. How do you think the capsid is released into the cytoplasm (3)? 4. Something is missing here (4). What do you think would happen that would allow the capsid to release the genome into the cytoplasm of the host cell? 5. Do you think this virus has a +sense or -sense genome? 6. The virus is unusual in that it buds from an internal membrane structure - not the plasma membrane. There also is a second membrane layer around the virus. Sketch out how you think that might happen. What do you think the second layer of membrane is all about (8)? 7. When the virus replicates its