Reovirus genomic segment S1, which has been implicated in the viral inhibition of cellular DNA synthesis, is transcribed into a single mRNA that encodes two proteins, the ∼ 49-kDa hemagglutinin, σ1, and the apparently nonstructural protein, p14. These two polypeptides have been expressed in mammalian cells, together or independently, in order to assess their role in the shutdown of host DNA replication. Results obtained with transient and stable expression systems demonstrate that production of serotype 3 σ1 and p14 together or individually is not sufficient to change the kinetics of DNA replication in uninfected cells. However, inhibition of DNA synthesis by reovirus type 1 infection was enhanced in cells producing type 3σ1 and p14 but not σ1 by itself. In addition, expression of p14 alone led to increased cytopathic effects following infection by either type 1 or type 3 virus. The results suggest that interactions with other viral components are required to elicit the effects of the S1-specified polypeptides on cellular DNA synthesis.
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