Disruption of the mouse Rce1 gene results in defective Ras processing and mislocalization of Ras within cells

Little is known about the enzyme(s) required for the endoproteolytic proces sing of mammalian Ras proteins. We identified a mouse gene (designated Rce1 ) that shares sequence homology with a yeast gene (RCE1) implicated in the proteolytic processing of Ras2p. To define the role of Rce1 in mammalian Ra s processing, we generated and analyzed Rce1-deficient mice. Reel deficienc y was lethal late in embryonic development (after embryonic day 15.5). Mult iple lines of evidence revealed that Rce1-deficient embryos and cells lacke d the ability to endoproteolytically process Ras proteins. First, Ras prote ins from Rce1-deficient cells migrated more slowly on SDS-polyacrylamide ge ls than Ras proteins from wild-type embryos and fibroblasts. Second, metabo lic labeling of Rce1-deficient cells revealed that the Ras proteins were no t carboxymethylated. Finally, membranes from Rce1 deficient fibroblasts lac ked the capacity to proteolytically process farnesylated Ha-Ras, N-Ras, and Ki-Ras or geranylgeranylated Ki-Ras. The processing of two other prenylate d proteins, the farnesylated G(gamma 1) subunit of transducin and geranylge ranylated Rap1B, was also blocked. The absence of endoproteolytic processin g and carboxymethylation caused Ras proteins to be mislocalized within cell s. These studies indicate that Reel is responsible for the endoproteolytic processing of the Ras proteins in mammals and suggest a broad role for this gene in processing other prenylated CAAX proteins.