CHARACTERIZATION OF THE MECHANISM OF CELLULAR AND CELL-FREE PROTEIN-SYNTHESIS INHIBITION BY AN ANTITUMOR RIBONUCLEASE

Onconase, a protein with anti-tumor activity, causes potent inhibition of protein synthesis in the rabbit reticulocyte lysate (IC(50)10(-11) M) and when microinjected into Xenopus oocytes (IC(50)10(-10)M). Oncon ase is a member of the RNase A superfamily; however, unlike RNase A, t he mechanism of protein synthesis inhibition does not involve apparent degradation of lysate or cellular ribosomal RNAs. Rather, reticulocyt e and oocyte tRNA is hydrolyzed after Onconase treatment. Furthermore, re-addition of tRNA to Onconase pretreated lysates or oocytes restore s the translational capacity of the system. Taken together these resul ts suggest that Onconase causes potent protein synthesis inhibition by a mechanism involving inactivation Of cellular tRNA. (C) 1994 Academi c Press, Inc.