The structural gene for a phosphorus-repressible phosphate permease in Neurospora crassa can complement a mutation in positive regulatory gene nuc-1

Robust and efficient synthetic method for forming DNA microarrays

The field of DNA microarray technology has necessitated the cooperative efforts of interdisciplinary scientific teams to achieve its primary goal of rapidly measuring global gene expression patterns. A collaborative effort was established to produce a chemically reactive surface on glass slide substrates to which unmodified DNA will covalently bind for improvement of cDNA microarray technology. Using the p-aminophenyl trimethoxysilane (ATMS)/diazotization chemistry that was developed, microarrays were fabricated and analyzed. This immobilization method produced uniform spots containing equivalent or greater amounts of DNA than commercially available immobilization techniques. In addition, hybridization analyses of microarrays made with ATMS/diazotization chemistry showed very sensitive detection of the target sequence, two to three orders of magnitude more sensitive than the commercial chemistries. Repeated stripping and re-hybridization of these slides showed that DNA loss was minimal, allowing multiple rounds of hybridization. Thus, the ATMS/diazotization chemistry facilitated covalent binding of unmodified DNA, and the reusable microarrays that were produced showed enhanced levels of hybridization and very low background fluorescence.

A putative rhamnogalacturonase required for sexual development of Neurospora crassa

In previous work, the asd-I (ascus development) gene of the filamentous fingus Neurospora crassa was identified as a gene expressed preferentially during the sexual cycle and shown to be essential for normal sexual development. The asd-I gene has been sequenced and further characterized. It contains two introns, the first of which is in-frame and inefficiently or differentially spliced. The predicted ASD-I protein has extensive homology with rhamnogalacturonase B of Aspergillus aculeatus, which cleaves the backbone within the ramified hairy regions of pectin. In homozygous asd-I crosses, sexual development is initiated and large numbers of normal-sized asci are formed. Ascospore delineation does not occur, however, and no sexual progeny are produced. As most asd-I asci contain eight nuclei, the two meiotic divisions and subsequent mitotic division typical of normal crosses seem to occur, but the haploid nuclei are not partitioned into ascospores. In wild-type crosses, the ASD-I protein is present in large amounts in croziers and young asci, but it is only faintly detectable in more mature asci containing developing ascospores. Models to explain the possible role of a rhamnogalacturonase in sexual development are presented.

NUC-2, a component of the phosphate-regulated signal transduction pathway in Neurospora crassa, is an ankyrin repeat protein

In response to phosphorus limitation, the fungus Neurospora crassa synthesizes a number of enzymes that function to bring more phosphate into the cell. The NUC-2 protein appears to sense the availability of phosphate and transmits the signal downstream to the regulatory pathway. The nuc-2+ gene has been cloned by its ability to restore growth of a nuc-2 mutant under restrictive conditions of high pH and low phosphate concentration. We mapped the cloned gene to the right arm of linkage group II, consistent with the chromosomal position of the nuc-2 mutation as determined by classical genetic mapping. The nuc-2' open reading frame is interrupted by five introns and codes for a protein of 1066 amino acid residues. Its predicted amino acid sequence has high similarity to that of its homolog in Saccharomyces cerevisiae, PHO81. Both proteins contain six ankyrin repeats, which have been implicated in the cyclin-dependent kinase inhibitory activity of PHO81. The phenotypes of a nuc-2 mutant generated by repeat-induced point mutation and of a strain harboring a UV-induced nuc-2 allele are indistinguishable. Both are unable to grow under the restrictive conditions, a phenotype which is to some degree temperature dependent. The nuc-2+ gene is transcriptionally regulated. A 15-fold increase in the level of the nuc-2+ transcript occurs in response to a decrease in exogenous phosphate concentration.

Analysis of the DNA-binding and dimerization activities of Neurospora crassa transcription factor NUC-1

NUC-1, a positive regulatory protein of Neurospora crassa, controls the expression of several unlinked target genes involved in phosphorus acquisition. The carboxy-terminal end of the NUC-1 protein has sequence similarity to the helix-loop-helix family of transcription factors. Bacterially expressed and in vitro-synthesized proteins, which consist of the carboxy-terminal portion of NUC-1, bind specifically to upstream sequences of two of its target genes, pho2+ and pho-4+. These upstream sequences contain the core sequence, CACGTG, a target for many helix-loop-helix proteins. A large loop region (47 amino acids) separates the helix I and helix II domains. Mutations and deletion within the loop region did not interfere with the in vitro or in vivo functions of the protein. Immediately carboxy-proximal to the helix II domain, the NUC-1 protein contains an atypical zipper domain which is essential for function. This domain consists of a heptad repeat of alanine and methionine rather than leucine residues. Analysis of mutant NUC-1 proteins suggests that the helix II and the zipper domains are essential for the protein dimerization, whereas the basic and the helix I domains are involved in DNA binding. The helix I domain, even though likely to participate in dimer formation while NUC-1 is bound to DNA, is not essential for in vitro dimerization.

Analysis of the DNA-binding and dimerization activities of Neurospora crassa transcription factor NUC-1

NUC-1, a positive regulatory protein of Neurospora crassa, controls the expression of several unlinked target genes involved in phosphorus acquisition. The carboxy-terminal end of the NUC-1 protein has sequence similarity to the helix-loop-helix family of transcription factors. Bacterially expressed and in vitro-synthesized proteins, which consist of the carboxy-terminal portion of NUC-1, bind specifically to upstream sequences of two of its target genes, pho2+ and pho-4+. These upstream sequences contain the core sequence, CACGTG, a target for many helix-loop-helix proteins. A large loop region (47 amino acids) separates the helix I and helix II domains. Mutations and deletion within the loop region did not interfere with the in vitro or in vivo functions of the protein. Immediately carboxy-proximal to the helix II domain, the NUC-1 protein contains an atypical zipper domain which is essential for function. This domain consists of a heptad repeat of alanine and methionine rather than leucine residues. Analysis of mutant NUC-1 proteins suggests that the helix II and the zipper domains are essential for the protein dimerization, whereas the basic and the helix I domains are involved in DNA binding. The helix I domain, even though likely to participate in dimer formation while NUC-1 is bound to DNA, is not essential for in vitro dimerization.

GLVR1, a receptor for gibbon ape leukemia virus, is homologous to a phosphate permease of Neurospora crassa and is expressed at high levels in the brain and thymus

The human gene GLVR1 has been shown to render mouse cells sensitive to infection by gibbon ape leukemia virus. This indication that the GLVR1 protein acts as a virus receptor does not reveal the protein's normal physiological role. We now report that GLVR1 is homologous to pho-4+, a phosphate permease of Neurospora crassa, at a level sufficiently high to predict that GLVR1 is also a transport protein, although the substrate transported remains unknown. To characterize the gene further, we have cloned cDNA for the mouse homolog of the gene, Glvr-1. The sequence of the murine protein differs from that of the human protein in 10% of residues, and it may be presumed that some of these differences are responsible for the inability of gibbon ape leukemia virus to infect mouse fibroblasts. Glvr-1 RNA is most abundant in mouse brain and thymus, although it is present in all tissues examined. The pattern of RNA expression found in mouse tissues was also found in rat tissues, in which the RNA was expressed at high levels in all compartments of the brain except the caudate nucleus and was expressed most abundantly early in embryogenesis. Thus, high-level expression of Glvr-1 appears to be restricted to specific tissues and may have developmental consequences.

Molecular analysis of nuc-1+, a gene controlling phosphorus acquisition in Neurospora crassa

In response to phosphorus starvation, Neurospora crassa makes several enzymes that are undetectable or barely detectable in phosphate-sufficient cultures. The nuc-1+ gene, whose product regulates the synthesis of these enzymes, was cloned and sequenced. The nuc-1+ gene encodes a protein of 824 amino acids with a predicted molecular weight of 87,429. The amino acid sequence shows homology with two yeast proteins whose functions are analogous to that of the NUC-1 protein. Two nuc-1+ transcripts of 3.2 and 3.0 kilobases were detected; they were present in similar amounts during growth at low or high phosphate concentrations. The nuc-2+ gene encodes a product normally required for NUC-1 function, and yet a nuc-2 mutation can be complemented by overexpression of the nuc-1+ gene. This implies physical interactions between NUC-1 protein and the negative regulatory factor(s) PREG and/or PGOV. Analysis of nuc-2 and nuc-1; nuc-2 strains transformed by the nuc-1+ gene suggests that phosphate directly affects the level or activity of the negative regulatory factor(s) controlling phosphorus acquisition.

Molecular analysis of nuc-1+, a gene controlling phosphorus acquisition in Neurospora crassa

In response to phosphorus starvation, Neurospora crassa makes several enzymes that are undetectable or barely detectable in phosphate-sufficient cultures. The nuc-1+ gene, whose product regulates the synthesis of these enzymes, was cloned and sequenced. The nuc-1+ gene encodes a protein of 824 amino acids with a predicted molecular weight of 87,429. The amino acid sequence shows homology with two yeast proteins whose functions are analogous to that of the NUC-1 protein. Two nuc-1+ transcripts of 3.2 and 3.0 kilobases were detected; they were present in similar amounts during growth at low or high phosphate concentrations. The nuc-2+ gene encodes a product normally required for NUC-1 function, and yet a nuc-2 mutation can be complemented by overexpression of the nuc-1+ gene. This implies physical interactions between NUC-1 protein and the negative regulatory factor(s) PREG and/or PGOV. Analysis of nuc-2 and nuc-1; nuc-2 strains transformed by the nuc-1+ gene suggests that phosphate directly affects the level or activity of the negative regulatory factor(s) controlling phosphorus acquisition.