Minimal promoter for the NAD+-specific glutamate dehydrogenase gene of Neurospora crassa

The expression of the NAD+-specific glutamate dehydrogenase (NAD-GDH) gene of Neurospora crassa is subject to catabolite repression. To identify the minimal sequence necessary for promoter function, the 5'-flanking region of the NAD-GDH gene was screened for potential protein-binding sites. Fragments of DNA, containing sequences upstream from the ATG initiation codon, were employed as probes of Southwestern blots of total cellular protein from cells grown in media promoting repression and induction of NAD-GDH. Two polypeptides interacted differentially with a promoter probe; one was present in greater abundance in repressed cells and a higher relative level of the second was witnessed in induced cells. Electrophoretic mobility shift assays with labeled promoter fragments exhibited preferential interaction with proteins in the induced cultures. The upstream sequence containing the putative protein-binding sites was fused with the coding sequence of the green fluorescent protein (GFP). The resulting plasmid was introduced into the microconidia of an albino mutant of N. crassa by electroporation. Stable integration of the plasmid and_expression of GFP in the hyphae and conidia of the transformants were demonstrated by Southern and Western blot analysis and fluorescence microscopy.

Sequence repeat-induced disruption of the major heat-inducible HSP70 gene of Neurospora crassa

The process of repeat-induced point mutation (RIP) was used to disrupt hsps-1, the gene encoding the major heat-inducible member of the HSP70 family of Neurospora crassa. A plasmid DNA, containing an incomplete copy of hsps-1 and the selectable marker qa-2+, was introduced into germinated conidia. The sexual progeny of transformants with ectopically integrated hsps-1 DNA was examined for RIP by Southern-blot analysis of MboI- and Sau3A-digested genomic DNA. Progeny strains, showing RIP, were tested for heat shock-responsive expression of hsps-1, by RNA-blot hybridization and Western-blot analysis, as well as for thermotolerance. Isolates with RIP showed low levels of hsps-1 mRNA and a lack of induction of HSP70 protein by heat shock, accompanied by only a marginal decrease in the acquisition of thermotolerance.

The hsp70 gene family of Neurospora crassa: cloning, sequence analysis, expression, and genetic mapping of the major stress-inducible member

The gene encoding the major heat shock-inducible member of the HSP70 family of Neurospora crassa was cloned and characterized. The 5' nontranscribed region shows the presence of consensus sequence motifs resembling the classical heat shock elements found in many heat shock-responsive eukaryotic promoters, as well as metal-responsive-element sequences. The coding region of the gene contains four introns with boundaries and internal consensus motifs typical of genes of filamentous fungi. None of the other stress-inducible hsp70 genes of fungal origin have, so far, been reported to contain introns. The sequence adjoining the transcriptional initiation zone shows the presence of prominent CT-rich stretches, characteristic of highly expressed fungal genes. The deduced amino acid sequence corresponds to a 646-residue polypeptide, with a calculated molecular mass of 70,561 Da and an average pI of 6.01, exhibiting strong sequence homology with many other eukaryotic HSP70s, with typical HSP70 family signatures 1 and 2 and a bipartite nuclear targeting sequence. Experiments with primer extension revealed the presence of one minor and two major transcriptional start sites. This gene, designated hsps-1, was mapped to a locus on the left arm of linkage group II, in close proximity to the AR-30 translocation breakpoint.

A Neurospora crassa heat-shocked cell lysate translates homologous and heterologous messenger RNA efficiently, without preference for heat shock messages

Cell-free protein synthesis systems were prepared from normally-grown (N-lysate) and heat-shocked (HS-lysate) Neurospora crassa mycelium. Although both lysates translated homologous mRNA, the HS-lysate was more active, yielding a higher incorporation of [35S]-methionine into hot TCA-insoluble material and a vastly superior protein synthesis profile. The optimal temperature for translation by both lysates was 21 degrees C; the HS-lysate did not translate heat-shock mRNA preferentially at any temperature tested. Fortuitously, heterologous messenger RNAs from diverse eukaryotic and viral sources - Drosophila, dog pancreas, rabbit globin mRNA, brome mosaic virus, tobacco mosaic virus - were translated by the HS-lysate with an efficiency comparable to that of the commercial rabbit reticulocyte system and superior to the wheat germ system. The cap analogues, m7G(5')ppp(5')G and m7G(5')Gm, inhibited translation significantly.

Expression of heat shock genes of Neurospora crassa: effect of hyperthermia and other stresses on mRNA levels

Neurospora crassa mycelium was heat shocked for intervals varying from 15-180 min. Heat shock mRNA was monitored by hybridization of Northern blots with the Drosophila hsp-70 gene probe and an inducible member of the yeast hsp-70 gene family, YG100. A 2.7 kilobase (kb) transcript, with homology to these two probes, was detected in cultures shocked for 15 min; its levels increased up to 60-90 min and declined thereafter. Sodium arsenite, too, induced the synthesis of this transcript. An additional, constitutively synthesized 2.4-kb transcript was revealed by hybridization with the yeast probe. The synthesis of this message was terminated during heat shock. Hybridization of Northern blots with the Drosophila actin gene probe demonstrated two size classes, 1.85 and 1.63 kb; the former decreased dramatically following heat shock. Recovery, as assessed by the disappearance of the 2.7-kb hsp-70-mRNA and restoration of the 1.85-kb actin message to the prestress levels, was essentially complete within 60 min of transfer to 28 degrees C. In vitro translations of RNA from stressed cells showed the heat shock messages to be stable and readily translatable. RNA of cells subjected to heat shock plus CdCl2 showed a higher content of messages for heat shock proteins of 70, 80, and 90 kilodaltons.