Acetate-nonutilizing mutants of Neurospora crassa: acu-6, the structural gene for PEP carboxykinase and inter-allelic complementation at the acu-6 locus

Summary Revertants of an acu-6 mutant of Neurospora crassa have been isolated. One revertant, which showed temperature-sensitive growth on acetate (Fig. 2), was found to possess an abnormally thermolabile PEP carboxykinase (Fig. 3). The temperature-sensitive property mapped at, or extremely close to, the site of the original mutation, confirming that acu-6 is the structural gene for PEP carboxykinase.A group of acu-6 mutants were examined by polyacrylamide gel electrophoresis for the presence of a protein migrating in the same position as PEP carboxykinase. Two of the seven mutants examined were found to possess such protein and both of these show inter-allelic complementation. When grown on acetate the complementing heterokaryons showed about 5% of the wild type level of PEP carboxykinase activity. This activity was more thermolabile than that in wild type (Fig. 6) and the heterokaryons showed temperature-sensitive growth on acetate (Fig. 5).