PROPERTIES OF THE CATALYTIC DOMAIN OF CDC25, A SACCHAROMYCES-CEREVISIAE GDP GTP EXCHANGE FACTOR - COMPARISON OF ITS ACTIVITY ON FULL-LENGTHAND C-TERMINAL TRUNCATED RAS2 PROTEINS/

Two C-terminal fragments (334 and 509 amino acid residues) of CDC25, a Saccharomyces cerevisiae GDP/GTP exchange factor, and the RAS2 protei n were purified from E. coli, using the pGEX system. With this method it was possible to avoid in part the proteolytic phenomena that usuall y convert full-length RAS2 (42kDa) into 37 and 30kDa forms. Of the two CDC25 fragments containing the conserved catalytic domain, only CDC25 -509 could enhance the guanine nucleotide exchange on RAS2. Comparison of the activities of RAS2-42/37kDa and RAS2-30kDa showed that the C-t erminal region (112 residues) influences neither the intrinsic GDP/GTP exchange nor its stimulation by CDC25-509. RAS2-42/37kDa was somewhat more effective in enhancing the adenylylcyclase activity of a yeast m embrane reconstituted system. CDC25-509 displayed a higher specific ac tivity than the catalytic domains of the two CDC25-like proteins: S. c erevisiae SDC25 and mouse CDC25m. (C) 1994 Academic Press, Inc.