DNA synthesis in heterokaryons formed by fusion of mammalian cells from different species

Abstract

Initiation and duration of DNA synthesis was studied in heterokaryons produced by virus-mediated fusion of cultured mammalian cells from different species. Synchronized HeLa cells were fused with synchronized Chinese hamster or mouse lines (whose phase times differed from those of HeLa cells), and DNA synthesis was studied in the nuclei of the heterokaryons. Initiation of DNA synthesis occurred apparently synchronously in the nuclei of HeLa-hamster and HeLa-mouse heterokaryons, and at a time corresponding to the shorter G1 period of the mouse or hamster parent, several hours before mononucleate HeLa cells entered the S phase. The duration of DNA synthesis, however, was found to be unchanged by association of nuclei having S periods of different lengths. Thus there is evidence for the operation of cytoplasmic factors in the control of initiation of DNA synthesis, but not in the regulation of the rate of chromosome replication.