Cis-acting and trans-acting regulatory mutations define two types of promoters controlled by the qa-1F gene of Neurospora

Systems biology of the qa gene cluster in Neurospora crassa

An ensemble of genetic networks that describe how the model fungal system, Neurospora crassa, utilizes quinic acid (QA) as a sole carbon source has been identified previously. A genetic network for QA metabolism involves the genes, qa-1F and qa-1S, that encode a transcriptional activator and repressor, respectively and structural genes, qa-2, qa-3, qa-4, qa-x, and qa-y. By a series of 4 separate and independent, model-guided, microarray experiments a total of 50 genes are identified as QA-responsive and hypothesized to be under QA-1F control and/or the control of a second QA-responsive transcription factor (NCU03643) both in the fungal binuclear Zn(II)2Cys6 cluster family. QA-1F regulation is not sufficient to explain the quantitative variation in expression profiles of the 50 QA-responsive genes. QA-responsive genes include genes with products in 8 mutually connected metabolic pathways with 7 of them one step removed from the tricarboxylic (TCA) Cycle and with 7 of them one step removed from glycolysis: (1) starch and sucrose metabolism; (2) glycolysis/glucanogenesis; (3) TCA Cycle; (4) butanoate metabolism; (5) pyruvate metabolism; (6) aromatic amino acid and QA metabolism; (7) valine, leucine, and isoleucine degradation; and (8) transport of sugars and amino acids. Gene products both in aromatic amino acid and QA metabolism and transport show an immediate response to shift to QA, while genes with products in the remaining 7 metabolic modules generally show a delayed response to shift to QA. The additional QA-responsive cutinase transcription factor-1β (NCU03643) is found to have a delayed response to shift to QA. The series of microarray experiments are used to expand the previously identified genetic network describing the qa gene cluster to include all 50 QA-responsive genes including the second transcription factor (NCU03643). These studies illustrate new methodologies from systems biology to guide model-driven discoveries about a core metabolic network involving carbon and amino acid metabolism in N. crassa.

The PAS/LOV protein VIVID supports a rapidly dampened daytime oscillator that facilitates entrainment of the Neurospora circadian clock

A light-entrainable circadian clock controls development and physiology in Neurospora crassa. Existing simple models for resetting based on light pulses (so-called nonparametric entrainment) predict that constant light should quickly send the clock to an arrhythmic state; however, such a clock would be of little use to an organism in changing photoperiods in the wild, and we confirm that true, albeit dampened, rhythmicity can be observed in extended light. This rhythmicity requires the PAS/LOV protein VIVID (VVD) that acts, in the light, to facilitate expression of an oscillator that is related to, but distinguishable from, the classic FREQUENCY/WHITE-COLLAR complex (FRQ/WCC)-based oscillator that runs in darkness. VVD prevents light resetting of the clock at dawn but, by influencing frq RNA turnover, promotes resetting at dusk, thereby allowing the clock to run through the dawn transition and take its phase cues from dusk. Consistent with this, loss of VVD yields a clock whose performance follows the simple predictions of earlier models, and overexpression of VVD restores rhythmicity in the light and sensitivity of phase to the duration of the photoperiod.

Nutritional and growth control of ribosomal protein mRNA and rRNA in Neurospora crassa

The effects of changing growth rates on the levels of 40S pre-rRNA and two r-protein mRNAs were examined to gain insight into the coordinate transcriptional regulation of ribosomal genes in the ascomycete fungus Neurospora crassa. Growth rates were varied either by altering carbon nutritional conditions, or by subjecting the isolates to inositol-limiting conditions. During carbon up- or down-shifts, r-protein mRNA levels were stoichiometrically coordinated. Changes in 40S pre-rRNA levels paralleled those of the r-protein mRNAs but in a non-stoichiometric manner. Comparison of crp-2 mRNA levels with those of a crp-2::qa-2 fusion gene indicated no major effect from changes in crp-2 mRNA stability. Crp-2 promoter mutagenesis experiments revealed that two elements of the crp-2 promoter, -95 to -83 bp (Dde box) and -74 to -66 bp (CG repeat) important for transcription under constant growth conditions, are also critical for transcriptional regulation by a carbon source. Ribosomal protein mRNA and rRNA levels were unaffected by changes in growth rates when the cultures were grown under inositol-limiting conditions, suggesting that, under these conditions, transcription of the ribosomal genes in N.crassa was regulated independently of growth rate.

Transformation of the oomycete pathogen Phytophthora megasperma f. sp. glycinea occurs by DNA integration into single or multiple chromosomes

A procedure for stable transformation was developed for Phytophthora megasperma f. sp. glycinea, an oomycete pathogen of soybean. Transformants were obtained using a bacterial hygromycin resistance gene fused to a promoter and terminator from the ham34 gene of another oomycete, Bremia lactucae. Vector DNA, alone or complexed to cationic liposomes, was introduced into protoplasts using polyethylene glycol and CaCl2. DNA and RNA hybridization, and phosphotransferase assays, confirmed the presence and expression of vector DNA in the transformants. Hybridization to electrophoretically separated chromosomes of P. m. glycinea showed that vector DNA had integrated into only one chromosome in four transformants, and into multiple chromosomes in one transformant.

The UAS(MAL) is a bidirectional promotor element required for the expression of both the MAL61 and MAL62 genes of the Saccharomyces MAL6 locus

Maltose fermentation in Saccharomyces yeasts requires one of five unlinked MAL loci: MAL1, 2, 3, 4, or 6. Each locus consists of three genes encoding maltose permease, maltase and the MAL activator. At MAL6 the genes are called MAL61, MAL62 and MAL63, respectively. Transcription of MAL61 and MAL62 is coordinately induced by maltose and repressed by glucose and this regulation is mediated by the MAL activator. By deletion analysis of the MAL61-MAL62 intergenic region, we show that a 68-basepair region, from base pairs -515 to -582 upstream of the MAL61 start codon, contains a sequence necessary for the maltose-induced expression of MAL61 and MAL62, the UAS(MAL). This sequence contains two copies of an 11-basepair dyad which may be the active elements of the UAS(MAL). Using heterologous gene plasmid constructs, we demonstrate that the UAS(MAL) sequence is sufficient for maltose inducibility of MAL62 and that this regulated expression requires a functional MAL activator. Our results suggest that the MAL61-MAL62 intergenic region contains additional distinct elements which function to precisely regulate MAL61 and/or MAL62 expression. Among these are repressing sequences, including a glucose-responsive element located between base pairs -583 and -638, which is partially responsible for mediating glucose-repression of MAL62 expression.

Coordinate expression of ribosomal protein genes in Neurospora crassa and identification of conserved upstream sequences

The relative levels of rRNAs and ribosomal proteins are coordinately regulated by growth rate and carbon nutrition in Neurospora crassa. However, little is known about the mechanisms involved. To investigate the transcriptional regulation of ribosomal protein genes in N. crassa, we cloned and sequenced a ribosomal protein gene (crp-3). The inferred crp-3 protein sequence shares 89% and 83% homology at its N-terminus with the yeast rp51 and the human S17 ribosomal proteins respectively. The crp-3 gene contains two introns, neither of which are conserved in position with the RP51 or the S17 genes. The crp-3 gene is present in a single copy and was mapped by RFLP analysis to the right arm of linkage group IV, near the cot-1 locus. Sequence comparisons of the upstream regions of the three sequenced crp genes revealed several common features. These include a 'Taq box' (consensus: ARTTYGACTT) at -39, a CG repeat (consensus: CCCRCCRRR) at -65, and a major transcription initiation site embedded in a purine rich region flanked by an upstream pyrimidine rich sequence. Using four N.crassa ribosomal protein genes as probes, we demonstrated that the levels of the four ribosomal protein mRNAs were closely coordinated during a nutritional downshift from sucrose to quinic acid.

Comparative studies of the quinic acid (qa) cluster in several Neurospora species with special emphasis on the qa-x-qa-2 intergenic region

The organization of the quinic acid (qa) genes in Neurospora crassa has been compared to that in several other Neurospora species. This gene cluster was found to be highly conserved in all species examined. However, there are numberous restriction fragment length polymorphisms that distinguish the heterothallic and homothallic species. Catabolic dehydroquinase assays indicated that qa-2 gene expression in the homothallic species is subject to induction by quinic acid, as is the case in N. crassa. The qa-x-qa-2 intergenic region of the homothallic species N. africana was cloned and sequenced. Conserved qa activator (qa-1F) binding sites have been identified in this region. When the qa-x-qa-2 intergenic region of N. crassa was replaced with its N. africana counterpart, qa-2 gene expression was reduced; however repression by glucose appeared normal. Furthermore, the N. africana start site for qa-2 transcription (which differs from the N. crassa start site) was utilized in the transformant. The overall evidence suggests that a weakening of the -120 activator binding site in the qa-x-qa-2 intergenic region may be responsible for these differences.

A Neurospora crassa ribosomal protein gene, homologous to yeast CRY1, contains sequences potentially coordinating its transcription with rRNA genes

We have isolated and sequenced a Neurospora crassa ribosomal protein gene (designated crp-2) strongly homologous to the rp59 gene (CRY1) of yeast and the S14 ribosomal protein gene of mammals. The inferred sequence of the crp-2 protein is more homologous (83%) to the mammalian S14 sequence than to the yeast rp59 sequence (69%). The gene has three intervening sequences (IVSs) two of which are offset 7 bp from the position of IVSs in the mammalian genes. None correspond to the position of the IVS in the yeast gene. Crp-2 was mapped by RFLP analysis to the right arm of linkage group III. The 5' region of the gene contains three copies of a sequence, the Ribo box, previously shown to be required for transcription of both 5S and 40S rRNA genes. We speculate that the Ribo box may coordinate ribosomal protein and rRNA gene transcription.

nit-2, the major positive-acting nitrogen regulatory gene of Neurospora crassa, encodes a sequence-specific DNA-binding protein

The nit-2 major nitrogen regulatory gene of Neurospora crassa turns on the expression of various unlinked structural genes that specify nitrogen-catabolic enzymes under nitrogen-limitation conditions. The nit-2 gene encodes a protein of 1036 amino acid residues with a single zinc finger and a downstream basic region that may make up a DNA-binding domain. The zinc-finger domain of the NIT2 protein was synthesized in two ways to examine its DNA-binding activity with gel-band-mobility shift and DNA-footprint experiments. The NIT2 protein binds to specific DNA recognition elements that are located upstream of nitrogen-regulated structural genes. Each recognition element contains at least two copies of a core sequence whose consensus is TATCTA.

Expression of cloned Saccharomyces diastaticus glucoamylase under natural and inducible promoters

Any one of three homologous genes - STA1, STA2 and STA3 - encoding glucoamylase isozymes I, II and III respectively, allows the Saccharomyces species to utilize starch as a sole carbon source. We show in this paper that glucoamylase II production can be increased 4-fold over the level produced by STA2 strains, by using a two-step fermentation and a yeast strain transformed with a high-copy-number plasmid carrying the STA2 gene. The accumulation of anomalous STA2 mRNA species, mainly differing at their 5' ends, and saturation of step(s) in the secretory pathway appear to be among the major factors limiting glucoamylase expression in synthetic media.

DNA sequence, organization and regulation of the qa gene cluster of Neurospora crassa

In Neurospora, five structural and two regulatory genes mediate the initial events in quinate/shikimate metabolism as a carbon source. These genes are clustered in an 18 x 10(3) base-pair region as a contiguous array. The qa genes are induced by quinic acid and are coordinately controlled at the transcriptional level by the positive and negative regulators, qa-1F and qa-1S, respectively. The DNA sequence of the entire qa gene cluster has been determined and transcripts for each gene have been mapped. The qa genes are transcribed in divergent pairs and two types of transcripts are associated with each gene: basal level transcripts that initiate mainly from upstream regions and are independent of qa regulatory gene control, and inducible transcripts that initiate downstream from basal transcripts and are dependent on qa-1F binding to a 16 base-pair sequence. We discuss how both types of transcription relate to the organization of the qa genes as a cluster and how this may impose constraints on gene dispersal.

Molecular cloning and analysis of the regulation of nit-3, the structural gene for nitrate reductase in Neurospora crassa

The nit-3 gene of Neurospora crassa encodes the enzyme nitrate reductase and is regulated by nitrogen catabolite repression and by specific induction with nitrate. The nit-3 gene was isolated from a cosmid-based genomic library by dual selection for benomyl resistance and for the ability to complement a nit-3 mutant strain using the sibling-selection procedure. The nit-3 gene was subcloned as a 3.8-kilobase DNA fragment from a cosmid that carried an approximately 40-kilobase N. crassa DNA insert. A restriction fragment length polymorphism analysis revealed that the cloned segment displayed tight linkage to two linkage-group-4 markers that flank the genomic location of nit-3. RNA gel blot analyses of RNA from wild-type and various mutant strains were carried out to examine the molecular mechanism for regulation of nit-3 gene expression. The nit-3 gene was transcribed to give a large mRNA of approximately 3.4 kilobases, the expected size to encode nitrate reductase. The nit-3 gene was only expressed in wild-type cells subject to simultaneous nitrogen derepression and nitrate induction. A mutant of nit-2, the major nitrogen regulatory gene of Neurospora, did not have detectable levels of nit-3 gene transcripts under the exact conditions in which these transcripts were highly expressed in wild type. Similarly, a mutant of nit-4, which defines a minor positive-acting nitrogen control gene, failed to express detectable levels of the nit-3 transcript. Nitrate reductase gene expression was partially resistant to nitrogen repression in a mutant of the nmr gene, which appears to be a regulatory gene with a direct role in nitrogen catabolite repression. Results are presented that suggest that the enzyme glutamine synthetase does not serve any regulatory role in controlling nitrate reductase gene expression.

Functional organization of the Aspergillus nidulans trpC promoter

We investigated the functional organization of the Aspergillus nidulans trpC promoter by the sequential removal of sequences upstream of the major trpC mRNA cap site (+1). DNA fragments containing promoter mutations were fused to the Escherichia coli lacZ gene, and a novel method was used to select for integration of the fusion gene at the Aspergillus argB locus. beta-Galactosidase assays and S1 nuclease protection experiments demonstrated that the promoter mutations affected gene expression in three ways: (i) 5' deletions up to -82 resulted in variable increases in beta-galactosidase activity, depending on the growth conditions; (ii) a deletion from -67 to -11 did not alter the level of beta-galactosidase activity, but did give rise to mRNAs with aberrant 5' ends; and (iii) a 5' deletion with an endpoint at -11 and an internal deletion from -142 to -11 abolished gene expression. These results indicate that sequences upstream of -82 reduce transcription of the trpC gene and that distinct DNA sequence elements are required for expression versus correct initiation of transcription of the trpC gene. The sequences essential for trpC expression do not include the common eucaryotic promoter elements CCAAT and TATAAA. To our knowledge, this is the first functional analysis of a promoter from a fungus other than Saccharomyces cerevisiae.

Functional organization of the Aspergillus nidulans trpC promoter

We investigated the functional organization of the Aspergillus nidulans trpC promoter by the sequential removal of sequences upstream of the major trpC mRNA cap site (+1). DNA fragments containing promoter mutations were fused to the Escherichia coli lacZ gene, and a novel method was used to select for integration of the fusion gene at the Aspergillus argB locus. beta-Galactosidase assays and S1 nuclease protection experiments demonstrated that the promoter mutations affected gene expression in three ways: (i) 5' deletions up to -82 resulted in variable increases in beta-galactosidase activity, depending on the growth conditions; (ii) a deletion from -67 to -11 did not alter the level of beta-galactosidase activity, but did give rise to mRNAs with aberrant 5' ends; and (iii) a 5' deletion with an endpoint at -11 and an internal deletion from -142 to -11 abolished gene expression. These results indicate that sequences upstream of -82 reduce transcription of the trpC gene and that distinct DNA sequence elements are required for expression versus correct initiation of transcription of the trpC gene. The sequences essential for trpC expression do not include the common eucaryotic promoter elements CCAAT and TATAAA. To our knowledge, this is the first functional analysis of a promoter from a fungus other than Saccharomyces cerevisiae.

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.

Constitutive and inducible Saccharomyces cerevisiae promoters: evidence for two distinct molecular mechanisms

his3 and pet56 are adjacent Saccharomyces cerevisiae genes that are transcribed in opposite directions from initiation sites that are separated by 200 base pairs. Under normal growth conditions, in which his3 and pet56 are transcribed at similar basal levels, a poly(dA-dT) sequence located between the genes serves as the upstream promoter element for both. In contrast, his3 but not pet56 transcription is induced during conditions of amino acid starvation, even though the critical regulatory site is located upstream of both respective TATA regions. Moreover, only one of the two normal his3 initiation sites is subject to induction. From genetic and biochemical evidence, I suggest that the his3-pet56 intergenic region contains constitutive and inducible promoters with different properties. In particular, two classes of TATA elements, constitutive (Tc) and regulatory (Tr), can be distinguished by their ability to respond to upstream regulatory elements, by their effects on the selection of initiation sites, and by their physical structure in nuclear chromatin. Constitutive and inducible his3 transcription is mediated by distinct promoters representing each class, whereas pet56 transcription is mediated by a constitutive promoter. Molecular mechanisms for these different kinds of S. cerevisiae promoters are proposed.

Recombinant DNA in filamentous fungi: progress and prospects

Recombinant DNA technology enables the creation of well-defined alterations in the genetic material of an organism. Methods to manipulate recombinant DNA in the filamentous fungi (a group of microorganisms that includes species of academic as well as commercial interest) have recently been developed. This has been the result of adaptation of procedures successfully employed in the manipulation of other microorganisms. There are a number of similarities in the behavior of recombinant DNA in different fungi, but a number of differences have also been observed between the filamentous and the nonfilamentous fungi. Such differences include the ability to identify DNA replication origins and the host range of expression of fungal genes.

Constitutive and inducible Saccharomyces cerevisiae promoters: evidence for two distinct molecular mechanisms

his3 and pet56 are adjacent Saccharomyces cerevisiae genes that are transcribed in opposite directions from initiation sites that are separated by 200 base pairs. Under normal growth conditions, in which his3 and pet56 are transcribed at similar basal levels, a poly(dA-dT) sequence located between the genes serves as the upstream promoter element for both. In contrast, his3 but not pet56 transcription is induced during conditions of amino acid starvation, even though the critical regulatory site is located upstream of both respective TATA regions. Moreover, only one of the two normal his3 initiation sites is subject to induction. From genetic and biochemical evidence, I suggest that the his3-pet56 intergenic region contains constitutive and inducible promoters with different properties. In particular, two classes of TATA elements, constitutive (Tc) and regulatory (Tr), can be distinguished by their ability to respond to upstream regulatory elements, by their effects on the selection of initiation sites, and by their physical structure in nuclear chromatin. Constitutive and inducible his3 transcription is mediated by distinct promoters representing each class, whereas pet56 transcription is mediated by a constitutive promoter. Molecular mechanisms for these different kinds of S. cerevisiae promoters are proposed.

Autogenous regulation of the positive regulatory qa-1F gene in Neurospora crassa

In Neurospora crassa, the qa-1F regulatory gene positively controls transcription of all genes in the quinic acid (qa) gene cluster. qa-1F is transcribed at a low, uninduced level but is subject to strong (50-fold), autogenous regulation as well as to control by the negative regulatory gene, qa-1S, and the inducer quinic acid. Cloned qa-1F DNA sequences hybridize to two related mRNAs of 2.9 and 3.0 kilobases. When wild-type (qa-1F+) cultures are transferred to inducing conditions, qa-1F mRNA increases for 4 h, remains somewhat level, and decreases after 8 to 10 h. That this control is autogenous, i.e., that the qa-1F gene controls the synthesis of its own mRNA, is indicated by the presence of approximately the same low level of qa-1F mRNA in poly(A)+ RNA from noninducible qa-1F- mutant cultures under inducing conditions as that observed in uninduced wild-type cultures. The qa-1S gene also regulates the transcription of qa-1F, since a qa-1S- mutant, whether in noninducing or inducing conditions, contains a level of qa-1F mRNA that corresponds to the low level observed in uninduced wild-type cultures. These results corroborate the hypothesis (M. E. Case and N. H. Giles, Proc. Natl. Acad. Sci. USA 72:553-557, 1975; V. B. Patel, M. Schweizer, C. C. Dykstra, S. R. Kushner, and N. H. Giles, Proc. Natl. Acad. Sci. USA 78:5783-5787, 1981; L. Huiet, Proc. Natl. Acad. Sci. USA 81:1174-1178, 1984) that the qa-1F gene encodes an activator protein and acts positively in controlling transcription of itself and the other qa genes.

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.

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

Transcriptional activation of the Neurospora crassa qa genes normally requires the positive regulatory gene, qa-1F+, whose function is controlled by the inducer quinic acid and by the product of the negative regulatory gene, qa-1S+. The properties of qa-1F+ activator have been examined in transcriptional mutations of the qa-2 structural gene, in which activator-independent transcription of qa-2 (qa-2ai mutants) occurs in strains having a qa-1F- gene. Seven qa-2ai mutants with DNA rearrangements in different 5' regions of qa-2 were analyzed in qa-1F+ strains. In five with rearrangements at position -190 or further upstream, expression of the qa-2 gene was inducible, and induction was accompanied by a change in the initiation site for transcription from position -45, characteristic of constitutive initiation in qa-2ai mutants to position +1, characteristic of the induced wild type. In two mutants with breakpoints at positions -86 and -53, qa-2 transcription initiated from upstream sequences within the rearrangements but not at the +1 site, and qa-2 expression was noninducible. The results indicate that (i) sequences between positions -190 and -86 are required for positive control of initiation at position +1, and (ii) negative control does not require sequences downstream of position -86. Additional evidence suggests that the product of the qa-1F+ gene in the noninduced state may also interact with distal upstream sequences positioned midway between divergently transcribed qa genes.

The qa repressor gene of Neurospora crassa: wild-type and mutant nucleotide sequences

The qa-1S gene, one of two regulatory genes in the qa gene cluster of Neurospora crassa, encodes the qa repressor. The qa-1S gene together with the qa-1F gene, which encodes the qa activator protein, control the expression of all seven qa genes, including those encoding the inducible enzymes responsible for the utilization of quinic acid as a carbon source. The nucleotide sequence of the qa-1S gene and its flanking regions has been determined. The deduced coding sequence for the qa-1S protein encodes 918 amino acids with a calculated molecular weight of 100,650 and is interrupted by a single 66-base-pair intervening sequence. Both constitutive and noninducible mutants occur in the qa-1S gene and two different mutations of each type have been cloned and sequenced. All four mutations occur within the predicted coding region of the qa-1S gene. This result strongly supports the hypothesis that the qa-1S gene encodes a repressor. All four mutations are located within codons for the last 300 amino acids of the qa-1S protein. The mutations in three of the mutants involve amino acid substitutions, while the fourth mutant, which has a constitutive phenotype, contains a frameshift mutation. The two constitutive mutations occur in the most distal region of the gene, possibly implicating the COOH-terminal region of the qa repressor in binding to its target. The two noninducible mutations occur in a region proximal to the constitutive mutations, possibly implicating this region of the qa repressor in binding the inducer.

The 3' splice site of pre-messenger RNA is recognized by a small nuclear ribonucleoprotein

A component present in splicing extracts selectively binds the 3' splice site of a precursor messenger RNA (pre-mRNA) transcript of a human beta-globin gene. Since this component can be immunoprecipitated by either autoantibodies of the Sm class or antibodies specifically directed against trimethylguanosine, it is a small nuclear ribonucleoprotein (snRNP). Its interaction with the 3' splice site occurs rapidly even at 0 degrees C, does not require adenosine triphosphate, and is altered by certain mutations in the 3' splice site region. Binding is surprisingly insensitive to treatment of the extract with micrococcal nuclease. The U5 particle is the only abundant Sm snRNP with a capped 5' end that is equally resistant to micrococcal nuclease. This suggests that, in addition to the U1 and U2 snRNP's, U5 snRNP's participate in pre-mRNA splicing.

Autogenous regulation of the positive regulatory qa-1F gene in Neurospora crassa

In Neurospora crassa, the qa-1F regulatory gene positively controls transcription of all genes in the quinic acid (qa) gene cluster. qa-1F is transcribed at a low, uninduced level but is subject to strong (50-fold), autogenous regulation as well as to control by the negative regulatory gene, qa-1S, and the inducer quinic acid. Cloned qa-1F DNA sequences hybridize to two related mRNAs of 2.9 and 3.0 kilobases. When wild-type (qa-1F+) cultures are transferred to inducing conditions, qa-1F mRNA increases for 4 h, remains somewhat level, and decreases after 8 to 10 h. That this control is autogenous, i.e., that the qa-1F gene controls the synthesis of its own mRNA, is indicated by the presence of approximately the same low level of qa-1F mRNA in poly(A)+ RNA from noninducible qa-1F- mutant cultures under inducing conditions as that observed in uninduced wild-type cultures. The qa-1S gene also regulates the transcription of qa-1F, since a qa-1S- mutant, whether in noninducing or inducing conditions, contains a level of qa-1F mRNA that corresponds to the low level observed in uninduced wild-type cultures. These results corroborate the hypothesis (M. E. Case and N. H. Giles, Proc. Natl. Acad. Sci. USA 72:553-557, 1975; V. B. Patel, M. Schweizer, C. C. Dykstra, S. R. Kushner, and N. H. Giles, Proc. Natl. Acad. Sci. USA 78:5783-5787, 1981; L. Huiet, Proc. Natl. Acad. Sci. USA 81:1174-1178, 1984) that the qa-1F gene encodes an activator protein and acts positively in controlling transcription of itself and the other qa genes.

Upstream promoter element of the human metallothionein-IIA gene can act like an enhancer element

Initiation of transcription by RNA polymerase II in eukaryotes is strongly increased by cis-acting genetic elements, known as activators or enhancers. Enhancers, first detected in simian virus 40 (SV40), were subsequently also found to control the expression of several cellular genes. The human metallothionein-IIA (hMT-IIA) gene, although inducible by heavy metals and glucocorticoids, is widely expressed in most cell types in the absence of inducers. Here we show that the high basal level of transcription of the hMT-IIA gene is due to the presence of an enhancer element within the hMT-IIA promoter region. The structural and functional organization of this cellular enhancer element in two direct repeats is strikingly similar to that of the enhancer element of SV40. This suggests a possible functional and evolutionary relationship between enhancers and upstream promoter elements.

Gene organization and regulation in the qa (quinic acid) gene cluster of Neurospora crassa

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Accurate transcription of cloned Neurospora RNA polymerase II-dependent genes in vitro by homologous soluble extracts

We have developed soluble extracts from Neurospora crassa capable of accurately initiating the transcription of cloned Neurospora protein-encoding genes by RNA polymerase II in vitro. The genes encoding glutamate dehydrogenase (am) and histones H3 and H4 were transcribed by the extracts, and transcription was sensitive to alpha-amanitin at 1 mg/ml. The 5' heterogeneity of the in vitro initiation reactions was highly specific. Of the 17 transcription initiation sites within the inducible qa gene cluster, only one minor site was used in vitro, suggesting that, in general, transcription from qa gene promoters requires at least one different protein from those required for transcription of the am and histone genes.

Structure of a Neurospora RNA polymerase I promoter defined by transcription in vitro with homologous extracts

A Neurospora in vitro transcription system has been developed which specifically and efficiently initiates transcription of a cloned Neurospora crassa ribosomal RNA gene by RNA polymerase I. The initiation site of transcription (both in vitro and in vivo) appears to be located about 850 bp from the 5' end of mature 17S rRNA. However, the primary rRNA transcripts are normally cleaved very rapidly at a site 120-125 nt from the 5' end in vitro and in vivo. The nucleotide sequence surrounding the initiation site has been determined. The region from -16 to +9 exhibits partial homology to the corresponding sequences from a wide variety of organisms including yeast, but the most striking similarity is to the initiation region from Dictyostelium discoideum which displays 73% homology to the Neurospora sequence from -23 to +47. The Neurospora sequences from -96 to +97 have been shown to be sufficient for transcription. This region contains two sequences displaying 8/9 bp matches to elements of the 5S rDNA promoter.

Genetic control of chromatin structure 5' to the qa-x and qa-2 genes of Neurospora

The roles of the qa-1F and qa-1S regulatory genes of Neurospora in modifying the chromatin structure of two qa structural genes have been studied by mapping DNase I hypersensitive sites in qa chromatin isolated from wild-type, qa-1F- (non-inducible) mutants, qa-1Sc (constitutive) mutants, qa-1S- (non-inducible) mutants, and from activator protein-independent mutants of qa-2 (qa-2ai). DNase I hypersensitive sites in the 5' region of the qa-x and qa-2 structural genes increase in number and sensitivity upon induction of transcription with quinic acid. Both qa-1F- and qa-1Sc mutations are associated with alterations in the DNase I sensitivity of the qa-x and qa-2 region, the latter mutations resulting in the common 5'-flanking region of these genes being accessible to DNase I. The qa-1F+ genotype is correlated with increased DNase I cleavage in the -200 to -88 region of qa-2, a region previously implicated in qa-1F regulation of RNA polymerase II access to the qa-2 promoters.

Molecular characterization of the qa-4 gene of Neurospora crassa

The qa-4 gene of Neurospora crassa encodes 3-dehydroshikimate dehydratase, which catalyzes the third step of the quinic acid (qa) catabolic pathway. The enzyme has previously been purified and characterized as a monomer of approx. 37 kDal. The nucleotide sequence of the qa-4 gene is presented here and the amino acid composition and tentative NH2-terminal sequence confirm the identification of the coding region within the qa-4 DNA sequence. There are no introns in the qa-4 coding region. By S1 nuclease mapping and primer extension analysis three distinct regions of transcription initiation were identified. Heterogeneity was also observed in the 3' ends of qa-4 mRNA. 5' and 3' untranslated regions of the qa-4 gene were compared with the corresponding regions in other Neurospora genes. Genomic blot analysis of twenty previously isolated qa-4 mutants revealed that two mutants, MC150 and MC191, have restriction patterns altered from wild type. In each strain the alteration occurs in the 3' half of the qa-4 coding region.

Accurate transcription of homologous 5S rRNA and tRNA genes and splicing of tRNA in vitro by soluble extracts of Neurospora

We have developed soluble extracts from Neurospora crassa capable of accurately and efficiently transcribing homologous 5S rRNA and tRNA genes. The extracts also appear to quantitatively end-process and splice the primary tRNA transcripts. Although the extracts could not transcribe a heterologous (yeast) 5S rRNA gene, they did transcribe a yeast tRNALeu gene and slowly process the transcripts. In addition, we have developed a novel strategy for rapidly sequencing uniformly labelled RNAs using base-specific ribonucleases. We have used this procedure to verify the identity of the in vitro transcripts and processing products.