The product of the regulatory gene of the proline catabolism gene cluster of Aspergillus nidulans is a positive-acting protein.

Eight new deletion mutations in the prn gene cluster involved in L-proline catabolism in Aspergillus nidulans have been characterised and mapped. Three of these are located within prnA, the regulatory gene mediating proline induction, and confirm the positive nature of the action of the prnA product. In addition, four prnA- alleles which are phenotypically suppressible by aminoglycoside antibiotics have been identified. Of these four phenotypically suppressible prnA- mutations, two have been tested for suppression by translational suppressors. Both are genotypically suppressible, showing that the prnA product must be a protein.