9.1 Insect Viruses Flashcards
Describe the structure of a polyhedra and its role in transmission of NPV virions
Polyhedra contain several virions and protect the virus in the external environment
How does a baculovirus infect a caterpillar?
The larval/caterpillar stage is the most susceptible to infection with NPV. However the host insect must ingest NPV’s to begin the infection process and occlusion bodies dissolve at a high pH for the virus to then be released and penetrate the host tissue.
Why does a baculovirus produce two variants in its life cycle?
It produces a budded virus which is produced in early infection and buds from the surface of the cell and infects neighbouring cells so it is then able to grow in cell culture.
It also produces an occluded virus which is produced during late infection and its where nucleocapsids assemble in the nucleus and acquire an envelope in the nucleus to be occluded there.
Why is the wild-type baculovirus an ineffective insecticide?
The infected insect will often take several days to weeks to die whilst the insect will continue to feed and cause economic damage to the crops
How has the baculovirus been engineered so that it is more effective as an insecticide?
Engineering to hasten death of the host insect and the foreign gene is assembled in a bacterial plasmid containing a small sequence derived from the viral genome
Why was the polyhedrin gene chosen as the site for inserting foreign genes in BEVS?
The insert of foreign DNA is downstream from the promoters for the polyhedrin or p10 genes and the strongest promoters are known for eukaryotic genes
Give two advantages of cloning a eukaryotic gene into BEVS compared to an E.coli expression vector
Strong expression of inserted gene and limitless size of the expressed protein
How is a foreign gene inserted into the baculovirus vector to obtain high levels of gene expression in insect cells?
The recombinant virus produced by co-transfection of the host cell with viral DNA and baculovirus transfer vector containing the foreign gene inserted between short sequences of viral DNA that bracket the cloning site in the polyhedrin gene
Why do viruses interfere with host cell apoptosis?
Most eukaryotic cells respond to viral infection and replication by undergoing programmed cell death aka apoptosis. Viruses counteract this by blocking apoptosis via two genes known as p35 and Iap
What is the significance of baculovirus gene p35 for the study of degenerative diseases in humans?
Gene p53 can prevent death of mammalian cells, this helps because mutant viruses induce very rapid cell death
