A SINGLE ARABIDOPSIS GF14 ISOFORM POSSESSES BIOCHEMICAL CHARACTERISTICS OF DIVERSE 14-3-3-HOMOLOGS

Arabidopsis cDNA clones of GF14 proteins originally were isolated on t he basis of their association with the G-box DNA/protein complex by a monoclonal antibody screening approach. GF14 proteins are homologous t o the 14-3-3 family of mammalian proteins. Here we demonstrate that re combinant GF14 omega, one member of the Arabidopsis GF14 protein famil y, is a dimeric protein that possesses many of the attributes of diver se mammalian 14-3-3 homologues. GF14 omega activates rat brain tryptop han hydroxylase and protein kinase C in a manner similar to the bovine 14-3-3 protein. It also activates exoenzyme S of Pseudomonas aerugino sa as does bovine brain factor activating exoenzyme S (FAS), which is itself a member of 14-3-3 proteins. In addition, GF14 omega binds calc ium, as does the human 14-3-3 homologue reported to be a phospholipase A2. These results indicate that a single isoform of this plant protei n family can have multiple functions and that individual GF14 isoforms may have multiple roles in mediating signal transductions in plants. However, GF14 omega does not regulate growth in an in vivo test for fu nctional similarity to the yeast 14-3-3 homologue, BMH1. Thus, while a single plant GF14 isoform can exhibit many of the biochemical attribu tes of diverse mammalian 14-3-3 homologues, open questions remain rega rding the physiological functions of GF14/14-3-3 proteins.