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, qutA4/qutA+ heterozygous diploids show semi-dominance of the mutant allele, giving markedly diminished growth on quinic acid and 30–40% decrease of enzyme induction. Strikingly, the qutA4/qutA8 heterozygous diploid grows to the same degree on quinic acid as the qutA4/qutA+ heterozygote 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 qalF, described for N. crassa may also reflect two regulatory genes.
ArmittS.,
McculloughW.,
RobertsC. F.1976; Analysis of acetate non-utilizing (acu) mutants in Aspergillus nidulans. Journal of General Microbiology 92:263–282
CaseM. E.,
GilesN. H.1975; Genetic evidence on the organization and action of the qa-1 gene product: a protein regulating the induction of three enzymes in quinate catabolism in Neurospora crassa. Proceedings of the National Academy ofSciences of the United States of America 72:553–557
ClutterbuckA. J.,
RopbrJ. A.1966; A direct determination of nuclear distribution in heterokaryons of Aspergillus nidulans. Genetical Research 7:185–194
HawkinsA. R.,
GilesN. H.,
Kinghorn.
1982; Genetical and biochemical aspects of quinate breakdown in the filamentous fungus Aspergillus nidulans. Biochemical Genetics 20:271–286
KinghornJ. R.,
HawkinsA. R.1982; Cloning and expression in Escherichia coli K12 of the biosynthetic dehydroquinase function of the aromcluster gene from the eukaryote Aspergillus nidulans. Molecular and General Genetics 186:145–152
KushnerS. R.,
HautalaJ. A.,
JacobsonJ. N.,
GilesN. H.,
VapnekD.1977; Expression of the structural gene for catabolic dehydroquinase of Neurospora crassa in Escherichia coli K12. Brookhaven Symposia in Biology 29:297–308
LittlewoodB. S.,
ChiaW.,
MetzenbergR. L.1975; Genetic control of phosphate-metabolising enzymes in Neurospora crassa: relationships among regulatory mutations. Genetics 79:419–434
QshdaaY.1982; Regulatory circuits for gene expression : the metabolism of galactose and phosphate. In The Molecular Biology of the Yeast Saccharomyces. Metabolism and Gene Expression pp. 159–180 Edited by
StrathemJ. N.,
JonesE. W.,
BroachJ. R.
New York: Cold Spring Harbor Laboratory;
PatelV. B.,
SchweizerM.,
DykstraC. C.,
KushnerS. R.,
GilesN. H.1981; Genetic organization and transcriptional regulation in the qagene cluster of Neurospora crassa. Proceedings of the National Academy of Sciences of the United States of America 78:5783–5787
PaytonM.,
McculloughW.,
RobertsC. F.1976; Agar as a carbon source and its effect upon utilization of other carbon sources by acetate nonutilizing(acu) mutants of Aspergillusnidulans. Journal of General Microbiology 94:228–233