IDENTIFICATION OF AF-6 AND CANOE AS PUTATIVE TARGETS FOR RAS

Ras (Ha-Ras, Ki-Ras, N-Ras) is implicated in the regulation of various cell functions such as gene expression and cell proliferation downstr eam from specific extracellular signals. Here, we partially purified a Ras-inter acting protein with molecular mass of about 180 kDa (p180) from bovine brain membrane extract by glutathione S-transferase (GST) Ha-Ras affinity column chromatography. This protein bound to the GTP g amma S (guanosine 5'-(3-O-thio)triphosphate, a nonhydrolyzable GTP ana log). GST-Ha-Ras affinity column but not to those containing GDP . GST -Ha-Ras or GTP gamma S . GST-Ha-Ras with a mutation in the effector do main (Ha-Ras(A38)). The amino acid sequences of the peptides derived f rom p180 were almost identical to those of human AF-6 that is identifi ed as the fusion partner of the ALL-1 protein. The ALL-1/AF-6 chimeric protein is the critical product of the t (6:11) abnormality associate d with some human leukemia. AF-6 has a GLGF/Dlg homology repeat (DHR) motif and shows a high degree of sequence similarity with Drosophila C anoe, which is assumed to function downstream from Notch in a common d evelopmental pathway. The recombinant N-terminal domain of AF-6 and Ca noe specifically interacted with GTP gamma S . GST-Ha-Ras. The known R as target c-Raf-1 inhibited the interaction of AF 6 with GTP gamma S . GST-Ha-Ras. These results indicate that AF-6 and Canoe are putative t argets for Ras.