Merck + Co., Inc.

Leonardo E Brizuela

Gary L Chrebet

Stephen Authur Parent

Keith A Bostian

Disclosed is a process utilizing yeast mutants for identifying active FK-506 type immunosuppressants. The process utilizes Saccharomyces cerevisiae mutants containing an fkr1, fkr2, fkr3 mutant gene or mixture thereof, which are resistant to FK-506 but sensitive to rapamycin. These mutants can be used in a diagnostic procedure for identifying FK-506 and FK-506 type immunosuppressants and in screening assays for compounds and fermentation broths which exhibit FK-506 type immunosuppressive activity. Specifically disclosed are the new yeast mutants, Saccharomyces cerevisiae YKF093, (Merck Culture Collection No. MY 2088) ATCC No. 74055, containing an fkr3 mutant gene, Saccharomyces cerevisiae YKF 012, (Merck Culture Collection No. MY 2096) ATCC No. 74061, which contains an fkr1 mutant gene, Saccharomyces cerevisiae YFK 014, (Merck Culture Collection No. MY 2097) ATCC No. 74062 and YFK-023-17A (Merck Culture Collection No. MY 2098) ATCC No. 74063, both which contain an fkr2 mutant gene and are useful in identifying active FK-506 type immunosuppressants.

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Heidelberg, Germany

Leonardo E Brizuela