The effects of exogenous proteins on the incorporation of [3H] thymidine into DNA was studied in Novikoff hepatoma ascites cells incubated in Eagle's minimal essential medium. A liver cytosol fraction (8 mg protein/ml) caused approximately 80% inhibition of isotope incorporation. The inhibitory activity of cytosol fractions from Morris hepatomas 9618A2, 5123C, and 20 were inversely related to their growth rate. Under conditions in which there appeared to be a density dependent inhibition of growth, a mean 10 to 20% stimulation of isotope incorporation was observed after addition of total calf thymus histones and individual fractions in the concentration range of 100 to 400 μg/ml. In experiments with lower cell concentrations, a 60% or greater increase in [3H] thymidine incorporation could be obtained with total calf thymus histone and with F1 and arginine rich histones from rat liver. At concentrations of 1 to 2 mg/ml, histones inhibited DNA synthesis. Bovine serum albumin had little effect on DNA synthesis. Polylysine caused an 80 to 90% inhibition at a concentration of 1 mg/ml, but stimulatory effects were detected under certain conditions at 10 μg/ml. The results suggest critical dependence on the ratio of cell and exogenous protein concentration in the action of proteins on DNA synthesis.
|Original language||English (US)|
|Number of pages||14|
|State||Published - 1976|
All Science Journal Classification (ASJC) codes
- Aquatic Science
- Cell Biology