Purity >97% by HPLC. Antifungal antibiotic with antitumour activity. A specific inhibitor of proteins containing nuclear export signal, it inhibits nucleo-cytoplasmic translocation of molecules such as the HIV-1 Rev protein and Rev-dependent export of mRNA. Other proteins that are influenced are actin, c-Abl, cyclin B1, MDM2/p53, I?B, MPF, and PKA. The suggested inhibition mechanism involves the direct binding to CRM1, which blocks the binding of CRM1 to proteins containing the nuclear export signal, via the interaction with cysteine residue in CRM1 control conserved region.