Isolation and characterization of revertant cell lines. IV. Direct selection of serum‐revertant sublines of SV40‐transformed 3T3 mouse cells

SV101, the SV40‐transformed subline of the mouse fibroblast line 3T3, is both serum‐ and density transformed, since it grows in both 1% and 10% calf serum, and grows beyond confluence in 10% calf serum. Negative selection at low cell density in 1% calf serum or in 10% agamma‐depleted serum permits direct recovery of serum‐revertant sublines of SV101. These sublines are unable to grow in 1% calf serum. Although negative selection at high cell density in 10% calf serum is known to permit recovery of density‐revertant sublines of SV101, most density‐revertants are not serum‐revertant. However, all serum‐revertants isolated so far are density‐revertant as well.