Growth-promoting alpha-globulin: A pleiotypic activator

Abstract Growth-promoting alpha-globulin (GPAG), a protein which induces mitotic activity in mammalian cells in vitro, has the capacity to stimulate increased incorporation of 3 H-uridine and 3 Hthymidine into RNA and DNA respectively, as determined by autoradiography. Marked enhancement of RNA and DNA synthesis was found in L cells in the presence of GPAG preincubated at 37 °C with tritium-labelled precursors. An increase in the incorporation of GPAG-bound precursors into macromolecules, parallel to the preincubation periods, was observed. GPAG stimulates the phosphorylation of nucleosides and/or the incorporation of nucleoside triphosphates into macromolecules so that its effect is not primarily on the cell membrane. It is suggested that GPAG can act as a pleiotypic activator.