Identification and location of the QUT genes in Aspergillus nidulans using DNA - mediated transformation.

A cluster of QUT genes within A. nidulans, encoding the enzymes required for the catabolism of quinate to protocatechuic acid, has previously been isolated within the recombinant phage Q1 by hybridization to certain genes in the equivalent N. crassa qa cluster. The location and functional integrity of the QUTE, QUTD and QUTA genes within the QUT gene cluster has been confirmed by the transformation of appropriate A. nidulans qut mutant strains. A.nidulans DNA homologous to the N. crassa qa-2 gene, encoding catabolic dehydroquinase, is able to transform a qutE mutant strain. Biochemical analysis of QUTE transformants containing multiple copies of the QUTE gene has shown that upon induction by quinate there is no increase in the level of catabolic dehydroquinase over that observed in a wild-type strain and that the transformants are subject to normal regulatory control. A. nidulans DNA homologous to the N. crassa qa-y gene is able to transform a qutD mutant strain. Biochemical studies of a number of qutD mutants suggests that in A.nidulans the QUTD gene encodes an essential component of a permease system required for the uptake of quinate. A.nidulans DNA homologous to the N. crassa qa-1F gene is able to transform a qutA mutant strain showing that the QUTA gene is equivalent to the N. crassa qa-1F gene and encodes a positively-acting regulatory protein. A small number of QUTA transformants exhibited constitutive expression of the QUT genes but these strains were subsequently found to be phenotypically unstable and therefore unsuitable for further analysis. DNA sequence analysis of the genes described above by the research group has confirmed their location within Q1 and their physical organisation in chromosome VIII of Aspergillus nidulans.