Isolated fractions of the growth-promoting alpha-globulin stimulate differently the incorporation of exogenous DNA into L cells.

The growth-promoting alpha-globulin necessary for long-term cultivation of mammalian cells in serum-free medium is a complex of several proteins which also stimulates the incorporation of exogenous DNA into recipient L cells. Biological activity responsible for the stimulation of DNA incorporation into L cells can be concentrated because one of two major protein components, compared to the whole GPAG complex, increases incorporation into cell nuclei by 100%.