Control of DNA synthesis in cells infected with polyoma virus

It had previously been established that cell DNA synthesis is inhibited in growing mouse embryo cells productively infected at high multiplicity with polyoma TSP1. In the present study it was found that cell DNA was stimulated in the same cell-virus system, but infected at low multiplicity (Branton and Sheinin, 1968). It was therefore concluded that the response of host cells to polyoma infection is dependent upon the multiplicity of infection. Stimulation of cell DNA synthesis was found to be associated with the formation late in the infectious cycle of cell DNA species of apparently lower molecular weight than that of normal cell DNA. In addition it was observed that the onset of polyoma capsid formation was delayed about 6 hours beyond the time at which viral DNA synthesis began. Earlier studies of cells infected at high multiplicity, in which cell DNA synthesis was blocked, indicated that capsid formation occurred at about the same time as did viral DNA synthesis. These observations suggested that regulation of cell DNA synthesis in polyoma-infected cells may be linked to capsid formation.