Leakage as the source of overgrowth stimulating activity in Rous sarcoma transformed cultures

The appearance of lactic dehydrogenase activity in the medium of Rous sarcoma cells was shown to accompany the appearance of overgrowth stimulating activity. The intracellular level of LDH was shown to increase in parallel with OSF as cultures became more transformed. Cells infected with non-transforming Rous associated virus did not differ from normal cells in this respect. It was concluded that the appearance of overgrowth stimulating activity in the medium is due to leakiness and that these changes are associated with transformation.