An "up-promotor" mutation affecting the acetamidase of Aspergillus nidulans.

A derivative of an areA200 strain of Aspergillus nidulans selected for strong growth on acetamide as the sole nitrogen source was found to have a mutation, amd-18, closely linked to amdS, the acetamidase structural gene. This mutation results in 2--3 fold higher acetamidase activities than wildtype strains in uninduced as well as induced cultures. The effects of the amd-18 mutation are superimposed on the effects of other regulatory mutations affecting the acetamidase. The amd-18 mutation is cis-dominant with respect to the amdS gene. Immunological and gel electrophoresis studies have shown that amd-18 strains produce higher levels of acetamidase protein. A previously described cis-dominant mutation, amdI9, also causes elevated levels of acetamidase protein. The amd-18 mutation may affect a promoter site for the amdS gene allowing an increased frequency of transcription.