Evidence for Two Control Genes Regulating Expression of the Quinic Acid Utilization (qut) Gene Cluster in Aspergillus nidulans

1984 Microbiology  
The first three steps in quinic acid degradation in Aspergillus nidulans are catalysed by highly inducible enzymes encoded by a gene cluster regulated by an adjacent control region. Analysis of two non-inducible mutants has been done in diploid strains, where qutA8 is recessive and all three enzyme activities are fully induced in heterozygous qutA8/qutA + diploids. In contrast, qutAl/qutA + heterozygous diploids show semi-dominance of the mutant allele, giving markedly diminished growth on
more » ... shed growth on quinic acid and 3040% decrease of enzyme induction. Strikingly, the qutABlqutA8 heterozygous diploid grows to the same degree on quinic acid as the qutA#/qutA + heteroqgote and shows the same level of enzyme induction, whereas both the homozygous mutant diploids do not grow on quinic acid and show no enzyme induction. Therefore the two mutant genomes complement, identifying two distinct regulatory gene functions. A genetic model is proposed of a negatively acting gene (qutA) repressing expression of a positively acting gene (qutD, previously designated qutA8+) whose product is in turn required for expression of the three structural genes. The qutA4 mutation is interpreted to produce an altered repressor insensitive to quinic acid, and the qutD8 mutation the loss of activator protein. Close similarity in the regulation of the quinic acid gene cluster in Neurospora crassa suggests that the two types of control mutation, qals and qal F, described for N. crassa may also reflect two regulatory genes. qut mutants (Hawkins et af., 1982) in the R21 genotype (patmA2 yA2) were crossed with strain R153 (wA3; pyroA4) to isolate R153 qut recombinants. In each case the mutant phenotype segregated as a Abbreviations: PMSF, phenylmethylsulphonyl fluoride; MA, minimal agar. METHODS Strains. Representative
doi:10.1099/00221287-130-3-567 pmid:6374025 fatcat:f6cls365lncu3gygqi6e66jk5i