ONCOGENIC RAS BLOCKS CELL-CYCLE PROGRESSION AND INHIBITS P34(CDC2) KINASE IN ACTIVATED XENOPUS EGG EXTRACTS

The effect of purified, bacterially expressed human Ras(H) proteins on embryonic cell cycle progression in activated Xenopus egg extracts wa s studied. Bacterially expressed human oncogenic Ras(H) protein is abl e to block the progression of the Xenopus embryonic cell cycle into M- phase. In contrast, the corresponding normal human Ras protein is rela tively ineffective when assayed in a like manner. The observed arresti ng activity can be blocked by the addition of Y13-259 anti-Ras monoclo nal antibody but not by nonspecific IgG. Oncogenic Ras also induces un ique morphological changes in the reconstituted nuclei; the nuclei app ear to be enlarged, and the chromatin partially condenses into fiber-l ike structures. This induced arrest is associated with suppression of p34(cdc2) kinase activity, indicating that the oncogenic Ras protein i nduces the arrest by inactivating p34(cdc2). This inactivation by onco genic Ras protein does not result from inhibition of the synthesis of cyclin B or of the binding of the newly synthesized cyclin B to the p3 4(cdc2).