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A Schaller

Publications and source records attributed to A Schaller.

At least 37 records · Page 2Linked to original sources
PubMed1999

A unique reaction in a common pathway: mechanism and function of chorismate synthase in the shikimate pathway.

Chorismate synthase, the seventh enzyme in the shikimate pathway, catalyzes the transformation of 5-enolpyruvylshikimate 3-phosphate to chorismate which is the last common precursor in the biosynthesis of numerous aromatic compounds in bacteria, fungi and plants. The enzyme has an absolute requirement for reduced FMN as a cofactor, although the 1,4-anti elimination of phosphate and the C(6proR)-hydrogen does not involve a net redox change. The role of the reduced FMN in catalysis has long been elusive. However, recent detailed kinetic and bioorganic approaches have fundamentally advanced our understanding of the mechanism of action, suggesting an initial electron transfer from tightly bound reduced flavin to the substrate, a process which results in C-O bond cleavage. Studies on chorismate synthases from bacteria, fungi and plants revealed that in these organisms the reduced FMN cofactor is made available in different ways to chorismate synthase: chorismate synthases in fungi--in contrast to those in bacteria and plants--carry a second enzymatic activity which enables them to reduce FMN at the expense of NADPH. Yet, as shown by the analysis of the corresponding genes, all chorismate synthases are derived from a common ancestor. However, several issues revolving around the origin of reduced FMN, as well as the possible regulation of the enzyme activity by means of the availability of reduced FMN, remain poorly understood. This review summarizes recent developments in the biochemical and genetic arena and identifies future aims in this field.

Catalysis↗
PubMed1999

Characterization of the subtilase gene family in tomato (Lycopersicon esculentum Mill.).

The gene family of subtilisin-like serine proteases (subtilases, SBTs) in tomato (Lycopersicon esculentum Mill.) comprises at least 15 members, 12 of which have been characterized in this study. Sequence comparison revealed that tomato subtilases fall into 5 distinct subfamilies. Single genes were shown to exist for LeSBT1, LeSBT2 and tmp), while 5 and 6 genes were found in the LeSBT3/4 and P69 subfamilies, respectively. With the exception of tmp, tomato subtilase genes were found to lack introns. Expression of subtilase genes was confirmed at the mRNA level by northern blot analysis and/or by primer extension experiments. For each of the 5 subtilase subfamilies, a distinctive pattern of expression was observed in tomato organs. At least one of the subtilases was found to be expressed in each organ analysed. Structural features evident from deduced amino acid sequences are discussed with reference to the related mammalian proprotein convertases.

Amino Acid Sequence↗
PubMed1999

Modulation of plasma membrane H+-ATPase activity differentially activates wound and pathogen defense responses in tomato plants.

Systemin is an important mediator of wound-induced defense gene activation in tomato plants, and it elicits a rapid alkalinization of the growth medium of cultured Lycopersicon peruvianum cells. A possible mechanistic link between proton fluxes across the plasma membrane and the induction of defense genes was investigated by modulating plasma membrane H+-ATPase activity. Inhibitors of H+-ATPase (erythrosin B, diethyl stilbestrol, and vanadate) were found to alkalinize the growth medium of L. peruvianum cell cultures and to induce wound response genes in whole tomato plants. Conversely, an activator of the H+-ATPase (fusicoccin) acidified the growth medium of L. peruvianum cell cultures and suppressed systemin-induced medium alkalinization. Likewise, in fusicoccin-treated tomato plants, the wound- and systemin-triggered accumulation of wound-responsive mRNAs was found to be suppressed. However, fusicoccin treatment of tomato plants led to the accumulation of salicylic acid and the expression of pathogenesis-related genes. Apparently, the wound and pathogen defense signaling pathways are differentially regulated by changes in the proton electrochemical gradient across the plasma membrane. In addition, alkalinization of the L. peruvianum cell culture medium was found to depend on the influx of Ca2+ and the activity of a protein kinase. Reversible protein phosphorylation was also shown to be involved in the induction of wound response genes. The plasma membrane H+-ATPase as a possible target of a Ca2+-activated protein kinase and its role in defense signaling are discussed.

Calcium↗
PubMed1998

Action of proteolysis-resistant systemin analogues in wound signalling.

In cultured cells of Lycopersicon peruvianum, the oligopeptide systemin which mediates systemic signalling in the tomato wound response is rapidly inactivated by proteolytic cleavage of the bond carboxy-terminal to Lys14. A systemin derivative in which this peptide bond had been modified by N-methylation was resistant to proteolytic inactivation. Systemin elicits a rapid, transient alkalinization of the growth medium in L. peruvianum cells. Consistent with its metabolic stability, the response elicited by the N-methylated peptide was found to be more sustained than that caused by systemin. In differentiated tomato plants, the stabilized peptide was found to be 3 times more active than systemin with respect to the induction of proteinase inhibitors I and II. This result indicates the possible physiological significance of the observed proteolytic degradation for systemin inactivation in planta. The activity of a protease capable of processing systemin carboxy-terminal of Lys14 was detected in tomato plasma membranes and may be responsible for the inactivation process. Two further peptides, N-methylated at the bonds carboxy-terminal of Gln3 and Arg10 had proteinase inhibitor inducing activities lower by a factor of 8 and 80, respectively, as compared to systemin. Correspondingly, the alkalinization response elicited by these two peptides in cultured cells was found to be more transient than the systemin response. The correlation between the duration of the alkalinization response and the proteinase inhibitor inducing activities of systemin analogues may be indicative of a casual relationship between ion fluxes and defense gene induction.

Amino Acid Sequence↗
PubMed1998

[Obstetrics--a gear in the machinery of history].

It was not Julius Caesar who was born by Caesarean section, as generally assumed, but Scipio Cornelius Africanus, who subdued Spain 100 years before Caesar's time. In chambers with walls of porphyrite, the Byzantine empresses used to give birth to the heirs to the throne. In England, the infertility of Queen Anne, who suffered from porphyria, led to the succession of the Protestant House of Hannover following the Catholic Stuarts. Christina of Sweden, called 'queen of baroque, rebel and scholar', was born in the 'caul'. At the age of 39 years, Johanna of Pfirt, married to Albrecht the Lame, secured the continuation of the Habsburg dynasty by giving birth to Rudolf the Founder. Maria Theresia, who had 16 children, was called 'mother-in-law of Europe'. She was delivered of her first child at the age of 19. The death of her sister Maria-Anna in childbed was one of the reasons why Gerard van Swieten was called to Vienna. Elisabeth of Württemberg, first wife of Franz I of Austria, died, not as a consequence of. but after a forceps operation carried out by Johann Lukas Boër. In England, Princess Charlotte, daughter of George IV, and her baby son died at the delivery; Sir Richard Croft, who had not used the forceps, committed suicide after this tragic incident. Being the next in succession, Victoria ascended the throne. The term 'narcose au chloroforme' (first used by James Young Simpson) was changed to 'narcose à la reine' after this method had been used at the birth of Victoria's eighth child by John Snow. It was Queen Victoria, who passed on haemophilia in European dynasties. When Marie Louise of Habsburg had her first child, Napoleon's son, the later Duke of Reichstadt, Antoine Dubois had to perform a turning of the transverse presentation and use the forceps on the head following after. The birth of Napoleon himself was a case of precipitate labour. Johann Klein, the successor of Boër, applied the forceps when Archduchess Sophie was delivered of her first child, the later Emperor Franz Joseph I of Austria, the first of the four 'salt princes'. The later Emperor Wilhelm II of Prussia was delivered by Eduard Arnold Martin the Elder, the obstetrician of Princess Victoria, the eldest daughter of Queen Victoria; the breech presentation became even more complicated by the raised arms of the child. Both latter monarchs had been 'asphyctic' after their birth. Johann Wolfgang von Goethe was also among those who were apparently dead after their birth.

Cesarean Section↗
PubMed1998

Functional importance of conserved nucleotides at the histone RNA 3' processing site.

Histone pre-mRNA 3' processing is controlled by a hairpin element preceding the processing site that interacts with a hairpin-binding protein (HBP) and a downstream spacer element that serves as anchoring site for the U7 snRNP. In addition, the nucleotides following the hairpin and surrounding the processing site (ACCCA'CA) are conserved among vertebrate histone genes. Single to triple nucleotide mutations of this sequence were tested for their ability to be processed in nuclear extract from animal cells. Changing the first four nucleotides had no qualitative and little if any quantitative effects on histone RNA 3' processing in mouse K21 cell extract, where processing of this gene is virtually independent of the HBP. A gel mobility shift assay revealing HBP interactions and a processing assay in HeLa cell extract (where the contribution of HBP to efficient processing is more important) showed that only one of these mutations, predicted to extend the hairpin by one base pair, affected the interaction with HBP. Mutations in the next three nucleotides affected both the cleavage efficiency and the choice of processing sites. Analysis of these novel sites indicated a preference for the nucleotide 5' of the cleavage site in the order A > C > U > G. Moreover, a guanosine in the 3' position inhibited cleavage. The preference for an A is shared with the cleavage/polyadenylation reaction, but the preference order for the other nucleotides is different [Chen F, MacDonald CC, Wilusz J, 1995, Nucleic Acids Res 23:2614-2620].

Animals↗
PubMed1997

Characterization of the calf thymus hairpin-binding factor involved in histone pre-mRNA 3' end processing.

Using ion exchange chromatography we have enriched the RNA hairpin-binding factor involved in histone pre-mRNA processing from calf thymus whole cell extract. We demonstrate that the interaction of the factor with its target RNA sequence, the hairpin structure located at the 3' end of mature histone mRNA, is sequence-specific and highly salt-resistant. We have developed a simple in vitro system which allows detection of activities stimulating histone pre-mRNA 3' end processing, based on mouse cell nuclear extract fractionated by Mono Q column chromatography. Using this system, we show that the bovine hairpin-binding factor participates in histone pre-mRNA 3' end processing in vitro. We have further purified the hairpin-binding factor in form of a RNA.protein complex by RNA-mediated elution from phosphocellulose. This led to a fraction highly enriched for 2 proteins of 40 and 43 kDa.

Animals↗
PubMed1997

The gene for histone RNA hairpin binding protein is located on human chromosome 4 and encodes a novel type of RNA binding protein.

The hairpin structure at the 3' end of animal histone mRNAs controls histone RNA 3' processing, nucleocytoplasmic transport, translation and stability of histone mRNA. Functionally overlapping, if not identical, proteins binding to the histone RNA hairpin have been identified in nuclear and polysomal extracts. Our own results indicated that these hairpin binding proteins (HBPs) bind their target RNA as monomers and that the resulting ribonucleoprotein complexes are extremely stable. These features prompted us to select for HBP-encoding human cDNAs by RNA-mediated three-hybrid selection in Saccharomyces cerevesiae. Whole cell extract from one selected clone contained a Gal4 fusion protein that interacted with histone hairpin RNA in a sequence- and structure-specific manner similar to a fraction enriched for bovine HBP, indicating that the cDNA encoded HBP. DNA sequence analysis revealed that the coding sequence did not contain any known RNA binding motifs. The HBP gene is composed of eight exons covering 19.5 kb on the short arm of chromosome 4. Translation of the HBP open reading frame in vitro produced a 43 kDa protein with RNA binding specificity identical to murine or bovine HBP. In addition, recombinant HBP expressed in S. cerevisiae was functional in histone pre-mRNA processing, confirming that we have indeed identified the human HBP gene.

Amino Acid Sequence↗
PubMed1996

Systemin--a polypeptide defense signal in plants.

Insect and pathogen attacks activate plant defense genes within minutes in nearby cells, and within hours in leaves far distant from the sites of the predator attacks. A search for signal molecules involved in both the localized and distal signalling has resulted in the identification of an 18-amino-acid polypeptide, called systemin, that activates defense genes in leaves of tomato plants when supplied at levels as low as fmols/plant. Several lines of evidence support a role for systemin as a wound hormone. As with animal polypeptide hormones, systemin is derived from a larger precursor protein, called prosystemin, by limited proteolysis. Systemin has been shown by autoradiography to be phloemmobile and, by antisense technology, to be an essential component of the wound-inducible, systemic signal transduction system leading to the transcriptional activation of the defensive genes. A search for the receptor of systemin has led to the identification in plant plasma membranes of a systemin-binding protein. However, this protein has properties not of a receptor, but of a furin-like proteinase that cleaves systemin into smaller polypeptides. Systemin and its precursor prosystemin provide prototypes for the emerging possibilities that polypeptide hormones may have broad roles in signalling environmental stress responses, and in regulating plant growth and development as well.

Abscisic Acid↗
PubMed1996

Molecular cloning of a tomato leaf cDNA encoding an aspartic protease, a systemic wound response protein.

A full-length cDNA encoding an aspartic protease (LeAspP) has been cloned from a tomato leaf cDNA library. Using LeAspP cDNA as a probe in gel blots, LeAspP mRNA was shown to be systemically induced in tomato leaves by wounding. Application of methyl jasmonate to leaves of intact tomato plants, or supplying systemin to young tomato plants through their cut stems, induces synthesis of LeAspP mRNA. LeAspP message is regulated in tomato similar to several systemic wound response proteins (swrps) that are part of the defense response in tomato plants directed against herbivore attacks.

Acetates↗
PubMed1996

Saccharomyces cerevisiae chorismate synthase has a flavin reductase activity.

Chorismate synthase (CS) catalyses the conversion of 5-enolpyruvylshikimate 3-phosphate (EPSP) to form chorismate, which is the last common intermediate in the synthesis of the three aromatic amino acids phenylalanine, tyrosine and tryptophan. Despite the overall redox-neutral reaction, catalysis has an absolute requirement for reduced flavin. In the fungus Neurospora crassa, a flavin reductase (FR) activity able to generate reduced flavin mononucleotide in the presence of NADPH is an intrinsic feature of a bifunctional CS. In all bacterial and plant species investigated to date, purified CSs lack an FR activity and are correspondingly 8-10 kDa smaller than the N. crassa CS (on the basis of SDS-PAGE). The cloning of N. crassa CS and subsequent characterization of the purified heterologously expressed enzyme indicates that, surprisingly, the FR probably resides within a region conserved amongst both mono- and bifunctional CSs and is not related to non-homologous sequences which contribute to the larger molecular mass of the N. crassa CS. This information directed this work towards the smaller Saccharomyces cerevisiae CS, the sequence of which was known, although the protein has not been extensively characterized biochemically. Here the characterization of the S. cerevisiae CS is reported in more detail and it is shown that the protein is also bifunctional. With this knowledge, S. cerevisiae could be used as a genetic system for studying the physiological consequences of bifunctionality. The phylogenetic relationship amongst known CSs is discussed.

Amino Acid Sequence↗
PubMed1996

[When children "have children"--reproduction biological problems in girls between 11 and 15 years of age].

The aim of the present study was to evaluate the obstetric risk in pregnant adolescents under 16 years of age. From July 1, 1970 to June 30, 1993, 188 girls aged 11-15 years were delivered at the 2nd Department of Obstetrics and Gynaecology, Vienna; 4569 primiparous women between 20 and 24 years with singleton pregnancies served as a control group. No significant differences between the two groups were found for the frequency of pregnancy-induced hypertension (2.1% vs. 3.5%), premature delivery rates (24.4% vs. 29.8%), percentage of babies weighing less than 2500 g (10.1% vs. 9.1%), mean birthweight (3082 g vs. 3117 g), frequency of intrauterine growth retardation (2.1% vs. 2.4%) and malformations (1.6% vs. 3.1%) and perinatal mortality to the end of the first week (1.1% vs. 0.5%). Adolescent mothers were found to have more spontaneous deliveries (85.1% vs. 74.9% in the control group, p < 0.005), lower Caesarean section rates (6.4% vs. 11.3%, p < 0.05) and fewer babies with a birthweight exceeding 4000 g (1.1% vs. 4.3%, p < 0.05). For the first time, the pregnancy outcome of European adolescents was studied over a period of 23 years. We conclude on the basis of our results that maternal and neonatal risk in mothers under 16 years of age does not exceed the obstetric risk in adult mothers.

Adolescent↗
PubMed1996

[Fracture of a surgical needle in suture management of episiotomy].

The complication of a break of the surgical needle during the suture of an episiotomy and the disappearance of the fragment in the perineal tissue has not been dealt with in the available literature. From our own material, a frequency of 0.17/1000 (n = 22,374) can be calculated. For the authors, the best method of coping with this complication is the removal of the needle fragment under a portable digital imaging system with two needleholders according to Bozemann.

Adult↗
PubMed1996

[Not Available].

Explore the source record for details and available documents.

General Surgery↗
PubMed1995

[Prenatal diagnosis of osteogenesis imperfecta. Report of a case classified as the classical Vrolik lethal type].

Report on prenatal sonographic diagnosis of osteogenesis imperfecta of the classical type "letalis Vrolik" in the case of a fetus in the 20th/21st week of pregnancy. The prenatal diagnosis of this kind of osteogenesis imperfecta is based on the soft membranous cranium (Caput membranacium), the microthorax caused by the bell-shaped configuration of the ribs and the diaphysis of the long bones which are too short for the age of pregnancy. These symptoms are first of all the consequence of a disturbed bone formation and mineralisation; its basis is a connatal deficit of collagen synthesis. The sonographic differential diagnosis to the type "Ekman Lobstein" of osteogenesis imperfecta and thanatophoric dwarfism are discussed.

Abortion, Eugenic↗
PubMed1995

Induction of wound response genes in tomato leaves by bestatin, an inhibitor of aminopeptidases.

Bestatin, an inhibitor of some aminopeptidases in plants and animals, is a powerful inducer of defense genes in tomato leaves; these genes are also induced by herbivore attacks, mechanical wounding, systemin, and methyl jasmonate. Unlike wounding and systemin, bestatin does not cause an increase in intracellular jasmonic acid concentrations, and inhibitors of the octadecanoid pathway do not inhibit induction by bestatin. Furthermore, defense genes were induced by bestatin in a mutant tomato line (JL-5) with a defect in the octadecanoid pathway. Bestatin therefore appears to be exerting its effects close to the level of transcriptional control of these genes, where it may be inhibiting a regulatory protease.

Aminopeptidases↗