Rearrangement mutations on the 5' side of the qa-2 gene of Neurospora implicate two regions of qa-1F activator-protein interaction

Induced expression of the Aspergillus nidulans QUTE gene introduced by transformation into Neurospora crassa

The qa-2 gene of Neurospora crassa encodes catabolic dehydroquinase which catabolizes dehydroquinic acid to dehydroshikimic acid. The QUTE gene of Aspergillus nidulans corresponds to the qa-2 gene of N. crassa. The plasmid pEH1 containing the QUTE gene from A. nidulans was used to transform a qa-2- strain of N. crassa. In Southern blot analyses, DNAs isolated from these transformants hybridized specifically to the QUTE gene probe. Northern blot analyses indicated that QUTE mRNA was produced in the transformants. The functional integrity of the QUTE gene in N. crassa was indicated by transformants which had regained the ability to grow on quinic acid as sole carbon source. Enzyme assays indicated that the specific activities of catabolic dehydroquinase induced by quinic acid in the transformants ranged from 4% to 32% of that induced in wild-type N. crassa. The evidence that the QUTE structural gene of A. nidulans is inducible when introduced into the N. crassa genome implies that the N. crassa qa activator protein can recognize, at least to a limited extent, DNA binding sequences 5' to the QUTE gene.

Expression of qa-1F activator protein: identification of upstream binding sites in the qa gene cluster and localization of the DNA-binding domain

The qa-1F regulatory gene of Neurospora crassa encodes an activator protein required for quinic acid induction of transcription in the qa gene cluster. This activator protein was expressed in insect cell culture with a baculovirus expression vector. The activator binds to 13 sites in the gene cluster that are characterized by a conserved 16-base-pair sequence of partial dyad symmetry. One site is located between the divergently transcribed qa-1F and qa-1S regulatory genes, corroborating prior evidence that qa-1F is autoregulated and controls expression of the qa-1S repressor. Multiple upstream sites located at variable positions 5' to the qa structural genes appear to allow for greater transcriptional control by qa-1F. Full-length and truncated activator peptides were synthesized in vitro, and the DNA-binding domain was localized to the first 183 amino acids. A 28-amino acid sequence within this region shows striking homology to N-terminal sequences from other lower-eucaryotic activator proteins. A qa-1F(Ts) mutation is located within this putative DNA-binding domain.

Expression of qa-1F activator protein: identification of upstream binding sites in the qa gene cluster and localization of the DNA-binding domain

The qa-1F regulatory gene of Neurospora crassa encodes an activator protein required for quinic acid induction of transcription in the qa gene cluster. This activator protein was expressed in insect cell culture with a baculovirus expression vector. The activator binds to 13 sites in the gene cluster that are characterized by a conserved 16-base-pair sequence of partial dyad symmetry. One site is located between the divergently transcribed qa-1F and qa-1S regulatory genes, corroborating prior evidence that qa-1F is autoregulated and controls expression of the qa-1S repressor. Multiple upstream sites located at variable positions 5' to the qa structural genes appear to allow for greater transcriptional control by qa-1F. Full-length and truncated activator peptides were synthesized in vitro, and the DNA-binding domain was localized to the first 183 amino acids. A 28-amino acid sequence within this region shows striking homology to N-terminal sequences from other lower-eucaryotic activator proteins. A qa-1F(Ts) mutation is located within this putative DNA-binding domain.

DNase I hypersensitive sites within the inducible qa gene cluster of Neurospora crassa

DNase I hypersensitive regions were mapped within the 17.3-kilobase qa (quinic acid) gene cluster of Neurospora crassa. The 5'-flanking regions of the five qa structural genes and the two qa regulatory genes each contain DNase I hypersensitive sites under noninducing conditions and generally exhibit increases in DNase I cleavage upon induction of transcription with quinic acid. The two large intergenic regions of the qa gene cluster appear to be similarly organized with respect to the positions of constitutive and inducible DNase I hypersensitive sites. Inducible hypersensitive sites on the 5' side of one qa gene, qa-x, appear to be differentially regulated. Employing these and previously published data, we have identified a conserved sequence element that may mediate the activator function of the qa-1F regulatory gene. Variants of the 16-base-pair consensus sequence are consistently found within DNase I-protected regions adjacent to inducible DNase I hypersensitive sites within the gene cluster.