Isolation and characterization of revertant cell lines. II. Growth control of a polyploid revertant line derived from SV40‐transformed 3T3 mouse cells

Abstract 3T3 mouse fibroblasts in 10% calf serum cease to increase in number at confluence. SV40‐transformed 3T3 cells lose their sensitivity to this growth control and so are able to reach multilayered cell densities. We previously described a polyploid revertant line F1SV101, isolated from a SV40‐transformed cell, that has a low maximum cell density (Pollack et al., '68), despite the continued presence in this revertant of SV40‐specific DNA, RNA and Tantigen. We have examined the mechanism by which the revertant maintains a low saturation density, and find that at confluence the revertant and 3T3 are both reduced in mitotic index, fraction of cells synthesizing DNA, and rate of DNA synthesis. The transformed cell does not respond to confluence. None of the lines sheds intact cells into the medium at confluence.