In order to isolate yeast proteins able to bind to the SH3 domain of the Cdc25p exchange factor, a biochemical approach was used. The SH3 (src homolog type 3) domain of yeast Cdc25p, fused both to a tail of 6 histidine (His) and to glutathione-S-transferase (GST), was purified and then, using His affinity for Ni2+ ions, bound to a Ni-NTA column. This column was used for isolating yeast proteins which have affinity for the yeast SH3-Cdc25p domain. The major protein thus isolated, was sequenced and identified as a yeast glyceraldehyde-3-phosphate dehydrogenase (GAP3DH).