AN ARABIDOPSIS IMMUNOPHILIN, ATFKBP12, BINDS TO ATFIP37 (FKBP INTERACTING PROTEIN) IN AN INTERACTION THAT IS DISRUPTED BY FK506

AtFKBP12 is an Arabidopsis cDNA that encodes a protein similar to the mammalian immunophilin, FKBP12. AtFKBP12 was used as 'bait' in a yeast 2-hybrid system to screen for cDNAs in Arabidopsis encoding proteins that bind to FKBP12. Two partial cDNAs were recovered encoding the C-t erminus of a protein we have called Arabidopsis thaliana FKBP12 intera cting protein 37 (AtFIP37). AtFIP37 is similar to a mammalian protein, FAP48, that also binds to FKBP12. The interaction between AtFKBP12 an d AtFIP37 in the 2-hybrid system, as assessed by histidine auxotrophy and P-galactosidase activity, was disrupted by FK506, but not by cyclo sporin A, a drug that binds to cyclophilin A. AtFIP37 was also shown t o bind in vitro to AtFKBP12 in GST-fusion protein binding assays. The binding was abolished by prior incubation of AtFKBP12 with FK506. Thes e findings indicate that an Arabidopsis FKBP12 ortholog encodes a prot ein that binds FK506 and that the interaction between AtFKBP12 and AtF IP37 may involve the FK506 binding site of AtFKBP12. The interaction p rovides interesting new opportunities for controlling protein:protein interactions in vivo in plants.