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3 Lytic Cycle of SV40 and Polyoma Virus

N. H. Acheson


Polyoma virus replicates in mouse cells; SV40 replicates in monkey cells. Infection of cells of other species leads to a variety of different responses. Cells can be semipermissive for viral replication. For example, when a population of hamster cells is infected with polyoma virus, only a very small fraction supports the replication of the virus. The other cells that take up virus synthesize some viral products, replicate their own DNA, and are stimulated to divide. However, after a few rounds of division, most of these cells (abortive transformants) cease dividing as the viral genome is lost; in a minority, the viral genome integrates into that of the cell and the continued expression of part of this viral genome causes the cell to continue to divide: it is stably transformed. Mouse cells are fully nonpermissive for SV40. Infection never leads to detectable virus replication; instead, most of the cells are abortively transformed and some are stably transformed. Abortive and stable transformations are discussed in Chapter 4; here we discuss the productive infection of permissive cells.

By 10–12 hours after the uptake of virus into cultured permissive cells, virus-coded early proteins, including T antigens, begin to appear (Fig. 3.1). Synthesis of a variety of cellular enzymes is induced, and replication of both cellular DNA and viral DNA takes place, beginning 12–15 hours after infection. Late viral mRNA is then made in large quantities, and viral capsid proteins are synthesized. Infectious virus begins to appear 20–25 hours after infection and...

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