The effect of growth-promoting alpha-globulin (GPAG) on the incorporation of exogenous DNA into L-cells. I. Incorporation of isologous and heterologous 3H-DNA.

Isologous and heterologous 3H-DNA (optimum concentration 25 microgram/ml of medium) are incorporated into L-cells from the medium during short-term incubation (up to 60 min). The incorporation of DNA is stimulated by a protein complex from calf serum--the growth-promoting alpha-globulin (GPAG) in the concentration 0.8 mg/ml of medium), which is rapidly taken into cells by pinocytosis. GPAG increases the frequency of incorporation of exogenous 3H-DNA into L-cells and the quantity of DNA incorporated. The quantity of 3H-DNA incorporated is further increased on the incubation of L-cells in a medium containing the complex 3H-DNA + GPAG, which is formed by the joint preincubation of the two components at 37 degrees C (20 hr); under these conditions the quantity of DNA incorporated is 150% greater than when 3H-DNA is used alone. GPAG acts as an activator of exogenous DNA transfer, stimulates its pinocytosis by the cells, and at the same time accelerates its intracellular transfer to the cell nuclei.