Search PubMed⌕ Search

Biomedical subjects

M J Hynes

Publications and source records attributed to M J Hynes.

At least 73 records · Page 4Linked to original sources
PubMed1989

Isolation and analysis of the acetate regulatory gene, facB, from Aspergillus nidulans.

The facB gene of Aspergillus nidulans is thought to be involved in acetate induction of enzymes required for acetate utilization and of the acetamidase encoded by the multiply regulated amdS gene. In addition, some evidence suggests that the facB gene has a structural as well as a regulatory role in acetate metabolism. The facB gene was cloned from a cosmid library by complementation of the facB101 loss-of-function mutation. Transformants receiving multiple copies of facB displayed stronger growth on acetamide media, indicating increased amdS expression, while growth on acetate was inhibited in these multicopy transformants. A 3.1-kilobase acetate-inducible facB transcript was detected by Northern (RNA) blot analysis. Examination of message levels in wild-type and mutant strains indicated that the facB gene is subject to carbon catabolite repression. Previous work has indicated that the presence of multiple copies of the 5' end of the amdS gene can result in titration of regulatory proteins. Additional copies of the facB gene were shown to specifically overcome the effect of facB product titration.

Acetates↗
PubMed1988

An amdS-lacZ fusion for studying gene regulation in Aspergillus.

A translational fusion has been constructed between the amdS gene of Aspergillus nidulans and the lacZ gene of Escherichia coli. Sequencing across the fusion junction confirmed the generation of an in-frame fusion at amino acid 34 of amdS and a novel protein has been detected in transformants carrying the fusion plasmid. Transformants of A. nidulans and Aspergillus niger carrying the fusion plasmid were obtained by co-transformation with a second selectable plasmid. These transformants were readily identified on media containing XGal. The intensity of the reaction on XGal media was indicative of the number of copies of the fusion plasmid carried by the transformants. The growth of highly expressing strains of A. nidulans was inhibited on XGal media. The fusion plasmid was used to develop a two-step gene replacement strategy in which the resident amdS gene was replaced with the fusion gene free of vector sequences. Plate tests and in vitro assays of the beta-galactosidase enzyme confirmed that expression of the fusion gene was regulated by amdS flanking sequences and trans-acting regulatory genes.

Amino Acid Sequence↗
PubMed1988

Identification of the sites of action for regulatory genes controlling the amdS gene of Aspergillus nidulans.

The amdS gene of Aspergillus nidulans, which encodes an acetamidase enzyme, is positively regulated by the trans-acting genes amdR, facB, amdA, and areA. Sequence changes in several cis-acting mutations in the 5' region of the gene which specifically affect amdS regulation were determined. The amdI9 mutation, which results in increased facB-dependent acetate induction, is due to a single-base change at base pair -210 relative to the start point of translation. The amdI93 mutation, which abolishes amdR-dependent omega-amino acid induction, is a deletion of base pairs -181 to -151. The amdI66 mutation, which causes increased gene activation in strains carrying amdA regulatory gene mutations, is a duplication of base pairs -107 to -90. Transformation of A. nidulans can generate transformants containing multiple integrated copies of plasmid sequences. When these plasmids carry a potential binding site for a regulatory gene product, growth on substrates whose catabolism requires genes activated by that regulatory gene can be reduced, apparently because of titration of the regulatory gene product. Introduction of 5' amdS sequences via cotransformation into strains of various genotypes was used to localize sequences apparently involved in binding of the products of the amdR, amdA, and facB genes. The position of these sequences is in agreement with the positions of the specific cis-acting mutations. Consistent with these results, a transformant of A. nidulans derived from a plasmid deleted for sequences upstream from -111 was found to have lost amdR- and facB-mediated control but was still regulated by the amdA gene. In addition, amdS expression in this transformant was still dependent on the areA gene.

Amidohydrolases↗
PubMed1988

Cloning and analysis of the positively acting regulatory gene amdR from Aspergillus nidulans.

The positively acting regulatory gene amdR of Aspergillus nidulans coordinately regulates the expression of four unlinked structural genes involved in acetamide (amdS), omega amino acid (gatA and gabA), and lactam (lamA) catabolism. By the use of DNA-mediated transformation of A. nidulans, the amdR regulatory gene was cloned from a genomic cosmid library. Southern blot analysis of DNA from various loss-of-function amdR mutants revealed the presence of four detectable DNA rearrangements, including a deletion, an insertion, and a translocation. No detectable DNA rearrangements were found in several constitutive amdRc mutants. Analysis of the fate of amdR-bearing plasmids in transformants showed that 10 to 20% of the transformation events were homologous integrations or gene conversions, and this phenomenon was exploited in developing a strategy by which amdRc and amdR- alleles can be readily cloned and analyzed. Examination of the transcription of amdR by Northern blot (RNA blot) analysis revealed the presence of two mRNAs (2.7 and 1.8 kilobases) which were constitutively synthesized at a very low level. In addition, amdR transcription did not appear to depend on the presence of a functional amdR product nor was it altered in amdRc mutants. The dosage effects of multiple copies of amdR in transformants were examined, and it was shown that such transformants exhibited stronger growth than did the wild type on acetamide and pyrrolidinone media, indicating increased expression of the amdS and lamA genes, respectively. These results were used to formulate a model for amdR-mediated regulation of gene expression in which the low constitutive level of amdR product sets the upper limits of basal and induced transcription of the structural genes. Multiple copies of 5' sequences from the amdS gene can result in reduced growth on substrates whose utilization is dependent on amdR-controlled genes. This has been attributed to titration of limiting amdR gene product. Strong support for this proposal was obtained by showing that multiple copies of the amdR gene can reverse this phenomenon (antititration).

Aspergillus nidulans↗
PubMed1987

Multiple copies of the amdS gene of Aspergillus nidulans cause titration of trans-acting regulatory proteins.

It has been established that a plasmid containing the amdS gene of Aspergillus nidulans may be used to transform amdS+ strains by selecting for increased utilization of acetamide as sole nitrogen source. Analysis of transformants has shown that multiple tandem copies of the plasmid can be integrated into the chromosome, commonly at sites other than the amdS locus. While the transformed phenotype was relatively stable through mitotic and meiotic divisions evidence was found for variation in plasmid copy number presumably due to unequal recombination events. Expression of the integrated amdS genes was related to copy number, and the amdS RNA produced was similar in size to wild-type RNA. Evidence for titration of the product of the regulatory gene amdR by multiple copies of amdS was found. No titration of the product of the areA gene was observed, and amdS expression was still dependent on areA function. Multiple copies of the amdI9 mutation resulted in poor growth on acetate. This was not observed in the case of the amdS+ gene. The cis-acting amdI9 mutation causes increased facB dependent acetate induction of amdS expression. Titration of the facB gene produce by amdI9 DNA, but not by amdS+ DNA, therefore suggested that the mutation results in increased affinity for the facB gene product.

Amidohydrolases↗
PubMed1987

The nucleotide sequence of the amdS gene of Aspergillus nidulans and the molecular characterization of 5' mutations.

The structure of the amdS gene of Aspergillus nidulans has been determined by nucleotide sequence analysis. The coding sequence is interrupted by three small introns with splicing signals consistent with other fungal genes. Possible TATA and CAAT elements are found upstream of the start point of transcription. Sequence changes in mutations in the 5' region of the gene have been determined. Two deletions including the start point of transcription abolish detectable transcripts. A series of mutations in the first exon cause frame shifts leading to polypeptide chain termination in the N-terminal region of the polypeptide. Levels of amdS RNA are reduced in these mutants indicating that translational termination can lead to decreased transcription or (more probably) to lower mRNA stability. The amdI18 mutation has properties consistent with it having a general up-promoter effect on amdS expression and results from a single base pair substitution approx. 77 bp upstream from the transcription start point.

Amidohydrolases↗
PubMed1987

Complementation of areA- regulatory gene mutations of Aspergillus nidulans by the heterologous regulatory gene nit-2 of Neurospora crassa.

Loss-of-function mutations in the regulatory gene areA of Aspergillus nidulans prevent the utilization of a wide variety of nitrogen sources. The phenotypes of nit-2 mutants of Neurospora crassa suggest that this gene may be analogous to the areA gene. Transformation has been used to introduce a plasmid containing the nit-2 gene into A. nidulans. The nit-2 gene of Neurospora complemented mutations in the areA gene, restoring the ability to use a variety of nitrogen sources. This indicated that the activator function of nit-2 and areA gene products was retained across these two fungal species. Southern blot analysis revealed both single-copy and multicopy integrations and, in at least one case, integration appeared to generate a nit-2 mutation. Integration of the transforming plasmid appeared to be by nonhomologous events at a number of different sites in the Aspergillus genome. The transformants were less sensitive to nitrogen-metabolite repression of extracellular protease activity and nitrate reductase (EC 1.6.6.3) than were wild-type A. nidulans. This indicated that nitrogen control was not completely normal in the nit-2 transformants.

Aspergillus nidulans↗
PubMed1985

Transformation of Aspergillus niger by the amdS gene of Aspergillus nidulans.

Aspergillus niger grows poorly on acetamide as a nitrogen or carbon source and lacks sequences detectably homologous to the amdS gene encoding the acetamidase of Aspergillus nidulans. We have taken advantage of these observations to develop a transformation system for A. niger using the amdS gene as a dominant heterologous marker for selecting transformants on the basis of acetamide utilization. Transformants varied in their ability to grow on amide media and the number of integrated copies of the amdS plasmid ranged from 1 or 2 to greater than 100. Southern analysis of transformants revealed that the multiple copies were integrated into the chromosome in tandem arrays. This result indicates that transformation of A. niger is more similar to mammalian cells than to yeast. Analysis of enzyme activity levels and RNA levels showed that most of the copies of amdS were expressed. Mitotic stabilities of transformants were found to be high. A transformant containing greater than 100 copies of the amdS gene was impaired in omega-amino acid utilization, a result that has also been found in A. nidulans. Since, in A. nidulans, omega-amino acids induce acetamidase via a characterizied regulatory gene (amdR/intA) this observation implies that titration of an analogous A. niger regulatory gene product by multiple amdS copies has occurred. Additional evidence suggested that the amdS gene is regulated in A. niger. It has also been shown that an unselected plasmid can be co-transformed with the amdS plasmid into A. niger.

Amidohydrolases↗
PubMed1985

Identification of the aciA gene controlled by the amdA regulatory gene in Aspergillus nidulans.

The amdA gene is one of a number of transacting regulatory genes controlling expression of the amdS gene in A. nidulans. A polypeptide of approximately 42,000 molecular weight has been found to be synthesized constitutively in amdA mutant strains and to be acetate inducible. A lambda clone containing a gene, called aciA, coding for this polypeptide has been isolated using differential screening with cDNA probes. Two acetate inducible RNA species have been identified by probing Northern blots with aciA containing probes. It is suggested that the amdA gene is a regulatory gene involved in acetate induction of aciA and amdS expression. The function of the aciA gene is not yet known.

Aspergillus nidulans↗
PubMed1983

99Mo metabolism in sheep after the intravenous injection of [99Mo] thiomolybdates.

[99Mo]di-, tri-, and tetrathiomolybdate (5.4 to 62.5 mg of Mo) were given by intravenous injection to sheep maintained on a sulfur-supplemented (3 g of S/kg) diet. All the compounds were metabolized very rapidly over the first 15 min postinjection, but relatively slowly thereafter, with a t1/2 of about 30 hr for dithiomolybdate and 40 h for tri- and tetrathiomolybdate. The [99Mo] metabolites present in plasma were identified by Sephadex G-25 chromatography. The main fate of the compounds injected appeared to be stepwise transformation to molybdate and subsequent rapid urinary elimination. Over 90-100 hr more than 90% of the radioactivity was excreted in urine, compared to less than 5% in the feces. The trichloroacetic acid (TCA) solubility of plasma copper and the diamine oxidase activity of ceruloplasmin was depressed, particularly over the first 15 min postinjection and a more persistant TCA-insoluble Cu fraction was apparent.

Animals↗
PubMed1983

Isolation of genomic clones containing the amdS gene of Aspergillus nidulans and their use in the analysis of structural and regulatory mutations.

Previous analysis of the amdS gene of Aspergillus nidulans has identified multiple regulatory circuits mediated by trans-acting regulatory genes, cis-acting mutations have been identified and shown to specifically affect individual regulatory circuits. Fine-structure genetic mapping of the amdS regions showed that these cis-acting mutations occur in a complex controlling region adjacent to the amdS structural gene. The amdS gene was cloned by differential hybridization, using cDNA probes derived from a high-level-producing strain and from a strain with a large amdS deletion mutation. RNA blotting experiments showed that a single RNA species of 1,600 to 1,700 base pairs is transcribed from the amdS gene. DNA blotting experiments on a large number of amdS mutant strains, including deletions and translocations, allowed the genetic and physical maps of the gene to be correlated. The controlling region of the gene is situated at the 5' end of the gene and the direction of transcription is toward the centromere of chromosome III. The regulatory mutations in the controlling region were found to be due to small-scale alterations in the DNA rather than to large-scale rearrangements resulting in gene fusions.

Amidohydrolases↗
PubMed1982

The binding of Ni2+ to adenylyl-3',5'-adenosine and to poly(adenylic acid).

Studies of the binding of Ni2+ to adenylyl-3',5'-adenosine (ApA) at pH 6.0 by ultraviolet spectrophotometry indicate the formation of a 1:1 complex in the presence of a large excess of metal ion. At 25 degrees C, and ionic strength mu = 0.5 M, the stability constant of Ni(ApA) is evaluated to be K = 2.6 (+/- 0.6) M-1. The low stability is taken as evidence that the predominant complex species is one in which the ApA acts as a monodentate ligand, mainly through the adenine group. The rate constants for complex formation and dissociation, kf = 1430 M-1 s-1 and kb =665 s-1 (25 degrees C, mu=0.5 M), determined by the temperature-jump relaxation technique, are consistent with this interpretation. The binding strength of Ni2+ to poly(adenylic acid) [poly(A)] has been studied at pH 7.0 using murexide as an indicator of the concentration of free Ni2+. Within the concentration range [Ni2+]free = 1 x 10(-5) -1 x 10(-3) M the data can be represented in the form of a linear Scatchard plot, i.e., the process can be described as the binding of Ni2+ to one class of independent binding sites. The number of binding sites per monomer is 0.26, and the stability constant K=8.2 x 10(3) M-1 (25 degrees C, mu=0.1 M). In kinetic studies of the reaction of Ni2+ with poly(A), two relaxation effects due to complex formation were detected, one with a concentration-independent time constant of about 0.4 ms, the other with a concentration-dependent time constant in the millisecond range. The concentration dependence of the longer relaxation time can be accounted for by a three-step mechanism which consists of a fast second-order association reaction followed by two first-order steps. There is evidence, however, that the overall process is more complicated than expressed by the three-step mechanism.

Adenosine Monophosphate↗
PubMed1982

A cis-dominant mutation in aspergillus nidulans affecting the expression of the amdS gene in the presence of mutations in the unlinked gene, amdA.

A mutant producing very high levels of the acetamidase enzyme encoded by the amdS gene has been isolated in a strain containing the amdA7 mutation, which itself causes high levels of this enzyme. Genetic analysis has shown that this mutation, designated amdI66, is adjacent to the amdS gene and is cis-dominant in its effect. The amdI66 mutation has little effect on amdS expression when present in strains not containing the amdA7 mutation. Two other amdA mutations investigated also interact with the amdI66 mutation to result in high acetamidase levels. No interaction between amdI66 and any of the other putative regulatory genes affecting amdS expression has been observed. The amdI66 mutation has been located by fine structure mapping at the extreme end of the controlling region, which has previously been defined by genetic mapping (HYNES 1979). Analysis of this region has been extended by mapping new mutations resulting in loss of amdS expression. One of these defines the most extreme site capable of mutation to loss of gene function found so far.

Amidohydrolases↗
PubMed1982

The regulation of NADP-linked isocitrate dehydrogenase in Aspergillus nidulans.

The regulation of NADP-linked isocitrate dehydrogenase (NADP-IDH) has been studied in wild-type and mutant strains of Aspergillus nidulans. In the wild-type strain studied, the levels of NADP-IDH vary in a similar way to those of acetamidase, acetyl-CoA synthase, isocitrate lyase and malate synthase under all growth conditions used. Similarly, fac mutants, which are altered in the regulation of these enzymes of acetate utilization, are affected in NADP-IDH levels in a parallel fashion, as are cre mutants, which show altered carbon catabolite repression of this group of enzymes. Possible functions of the NADP-IDH enzyme are considered.

Acetate-CoA Ligase↗
PubMed1982

L-histidine utilization in Aspergillus nidulans.

Histidase activity rather than uptake of L-histidine is the limiting factor for the utilization of histidine as the sole nitrogen source for Aspergillus nidulans. Histidine cannot act as the sole carbon source, and evidence is presented indicating that this is attributable to an inability to convert histidine to L-glutamate in vivo. It has been shown that this fungus lacks an active urocanase enzyme and that histidine is quantitatively converted to urocanate, which accumulates in the extracellular medium. The use of histidine as a nitrogen source is regulated by nitrogen metabolite repression control of histidase synthesis. In addition, evidence for a requirement for a carbon source for histidase synthesis and for a minor form of control by nitrate is presented. The activity of the histidase enzyme is inhibited by micromolar concentrations of the product urocanate and by physiological levels of L-glutamate and L-glutamine.

Ammonia-Lyases↗
PubMed1981

The regulation of phosphoenolpyruvate carboxykinase and the NADP-linked malic enzyme in Aspergillus nidulans.

It has previously been suggested that the synthesis of phosphoenolpyruvate carboxykinase (EC 4.1.1.32) in Aspergillus nidulans is regulated by a repression-derepression mechanism involving a glycolytic intermediate, and not by induction. Results obtained using compounds that enter the tricarboxylic acid cycle via 2-oxoglutarate, and that can supply both a carbon and a nitrogen source for A. nidulans, suggest it is more likely that the synthesis of phosphoenolpyruvate carboxykinase is inducible, and only weakly regulated by carbon catabolite repression. a similar study of the regulation of the NADP-linked malic enzyme (EC 1.1.1.40) indicates that it too may be inducible.

Aspergillus nidulans↗
PubMed1981

The therapeutic advantages of a balanced nutritional support system.

Twenty-two critically ill patients were entered into a 21-day prospective study to evaluate the feasibility of relying on a balanced nutritional support system to satisfy the needs of a diverse group of surgical patients. No patient sustained a serious complication related to glucose metabolism, and only two patients required insulin. Twenty-one of the patients achieved positive nitrogen balance during the study, and 13 had a significant weight gain not related to water retention. Documented sepsis was present in 50% of the patients but in spite of this, 91% had a successful course of therapy. The ease of management and metabolic efficiency of this approach encourages the use of fat as a primary energy substrate in a balanced nutritional support system to restore positive energy and nitrogen balance.

Adult↗