Interleukin 3 (IL-3) stimulates several biochemical and biological responses in IL-3-dependent tissue culture cells. We examined the possibility that guanyl nucleotide regulatory (G) proteins may transduce signals from IL-3 receptors. We report here that pertussis toxin (PT), which can covalently modify a subclass of G proteins, is capable of inhibiting IL-3-stimulated proliferation in a dose-dependent fashion. PT inhibition of IL-3-stimulated proliferation could be overcome by using the Ca++ ionophore A23187 in conjunction with TPA. PT could also inhibit IL-3-stimulated hexose transport. In the absence of IL-3, hexose transport could be stimulated by introducing GTP-gamma S into intact cells. From these data we propose that IL-3 receptors transduce signals via a PT-sensitive G protein(s).

The polypeptide chain of folylpolyglutamate synthetase from beef liver has been isolated and partially characterized. This polypeptide has an apparent molecular weight of 73,000. Its amino-terminal residue is blocked. Amino acid analysis agrees with the hydrophobic properties and the pI (6.0) of this cytosolic enzyme. Polyclonal antibodies to the denatured enzyme have been prepared.