Analysis of acetate non-utilizing (acu) mutants in Aspergillus nidulans.

Genetic analysis of 119 acetate non-utilizing (acu) mutants in Aspergillus nidulans revealed ten new loci affecting acetate metabolism in addition to the three previously recognized on the basis of resistance to fluoroacetate and acetate non-utilization. The enzyme lesions associated with mutations at seven of the acu loci are described. These are: facA (= acuA), acetyl-CoA synthase; acuD, isocitrate lyase; acuE, malate synthase; acuF, phosphoenolpyruvate carboxykinase; acuG, fructose 1,6-diphosphatase; acuK and acuM, malic enzyme. The acu loci have been mapped and are widely distributed over the genome of A. nidulans. Close linkage has only been found between acuA and acuD (less than 1% recombination). There is no evidence for any pleiotropic mutation in that region affecting the expression of both these genes. Poor induction of the enzymes of the glyoxylate cycle, isocitrate lyase and malate synthase in mutants lacking acetyl-CoA synthase, and also in the other two classes of fluoroacetate-resistant mutants, indicates that the inducer, acetate, may be metabolized to a true metabolic inducer, perhaps acetyl-CoA, to effect formation of the enzymes. There is no evidence of any other class of pleiotropic recessive acu mutations affecting the expression of the acuD and acuE genes, which are therefore thought to be subject to negative rather than positive control.