AMINO-ACID-RESIDUES IN THE CDC25 GUANINE-NUCLEOTIDE EXCHANGE FACTOR CRITICAL FOR INTERACTION WITH RAS

Previously we found that negatively charged residues at positions 62, 63, and 69 of H-Ras are involved in binding to the CDC25 guanine nucle otide exchange factor (GEF). Using site-directed mutagenesis, we have changed conserved, positively charged residues of CDC25(GEF) to glutam ic acid. We find the nonfunctional CDC25(R1374E) mutant and the nonfun ctional H-Ras(E63K) mutant cooperate in suppression of the loss of CDC 25 function in Saccharomyces cerevisiae. Also, peptides corresponding to residues 1364 to 1383 of CDC25(GEF) inhibit interaction between GEF s and H-Ras. We propose that residues 1374 of CDC25(GEF) and 63 of H-R as farm an ion pair and that when this ion pair is reversed, functiona l interaction can still occur.