Molecular cloning of Saccharomyces cerevisiae MLF4/SSH4 gene which confers the immunosuppressant leflunomide resistance.

Immunosuppressant leflunomide inhibits the growth of cytokine-stimulated lymphoid cells in vitro and also inhibits the growth of eukaryotic microorganism Saccharomyces cerevisiae. To elucidate the molecular mechanism of the action of the drug, a yeast gene which suppresses the anti-proliferative effect when in increased copy number was cloned and designated MLF4 for multicopy suppressor of leflunomide sensitivity. DNA sequencing analysis indicates that the MLF4 gene is identical to the SSH4 gene which suppresses the shr3 mutation. Excess of amino acids overcame the anti-proliferative activity of leflunomide. Thus, leflunomide is suggested to affect amino acid transport by interacting with Shr3 chaperon-like protein.