Activation of the ras oncogene has been implicated as the causative agent in as many as 30% of all human tumors. Yet in spite of extensive work on the ras gene, almost nothing is known about the biochemical function of the ras proteins. A recently characterized protein, the ADP-ribosylation factor or ARF, is a component of the adenylate cyclase system and shares several features with ras, p21 including size, location, and the ability to bind GTP. Characterization of the binding and hydrolysis of guanine nucleotides by ras and ARF will be undertaken. A systematic search will then be conducted to identify factor(s) which increase either the exchange or hydrolysis of guanine nucleotides by these regulatory proteins. The assays developed in these studies will also be used to help define the function of specific genes, identified in yeast as suppressors or activators of ARF disruption. These studies should help locate cellular targets for these regulatory proteins and may identify the physiological role of these proteins in cellular metabolism or proliferation.