Viruses From Animal and Plants
Negative strand ssRNA viruses need to have a preformed replicase when they invade a mammalian cell because they

have to make a positive strand copy that can be translated
use it to terminate transcripts when they copy host cell mRNA
None of these
use it to modify host enzymes that are recruited for viral replication

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Viruses From Animal and Plants
Influenza virus undergoes antigenic shift resulting in major antigenic changes by which of the following mechanisms?

Reassortment of RNA segments from different influenza viruses
Somatic recombination of heavy and light chains
Changing the receptor binding canyon that docks with the host receptor
Expression of several different capsule types

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