On the localization of FKBP25 in T-lymphocytes.

Using polyclonal rabbit antibodies against bovine FKBP25, NEPHGE/SDS-PAGE and Western blotting we demonstrate that the rapamycin-specific immunophilin FKBP25 is present in T-lymphoma Jurkat cells. Subsequent fractionations of the soluble Jurkat cell proteins have revealed that FKBP25 predominantly occurs in the nuclear fraction. FKBP25 has the ability to bind to DNA. The FKBP25/DNA complex can be dissociated in the presence of a high salt concentration. FKBP12, which shares high amino acid sequence homology to the C-terminal domain of FKBP25, has no tendency to bind to DNA. CD-constrained predictions of the secondary structures in FKBP25 suggest that an amphipathic helix-loop-helix occurs in the N-terminal part of the protein and may account for its binding to DNA.