Reactivation of G₀ nuclei by S-phase cells

tsAF8 cells are a temperature sensitive (ts) mutant of BHK that arrest in G₁ at the nonpermissive temperature or after serum deprivation. G₀ tsAF8 were fused by polyethylene glycol with other G₀ tsAF8 cells, and the fusion products were incubated at the nonpermissive temperature. The homokaryons were incapable of entering S phase under these conditions. However, when S phase tsAF8 cells were fused with G₀ tsAF8 cells, both nuclei in the homokaryons entered S phase, even when the fusion products were incubated at the nonpermissive temperature. In addition S phase tsAF8 cells, if fused with chick erythrocytes, can reactivate the chick nucleus, even if the heterokaryons are placed at nonpermissive temperature. Therefore S phase information of tsAF8 can induce DNA synthesis, after fusion, in mammalian G₀ AF8 cells and chick erythrocytes even when the homokaryons or heterokaryons are incubated at the nonpermissive temperature.