Inhibition of DNA synthesis in cultures of 3T3 cells by isolated surface membranes.

Abstract
When added to a sparse culture of 3T3 [mouse fibroblasts] cells, a surface membrane-enriched fraction from 3T3 cells inhibited rate of DNA synthesis in a time- and concentration-dependent manner. Membrane preparation had no effect on rate of DNA synthesis of SV 40-transformed 3T3 cells. A similar membrane preparation from transformed cells had a lesser inhibitory effect on 3T3 cells and no effect on transformed cells. The inhibition by membranes were reversible. When added to growing 3T3 cells, 3T3 surface membranes may mimic the effect of increasing cell density on DNA synthesis.