The sporulation-specific enzymes encoded by the DIT1 and DIT2 genes catalyze a two-step reaction leading to a soluble LL-dityrosine-containing precursor of the yeast spore wall

Dityrosine is a sporulation-specific component of the yeast ascospore wall that is essential for the resistance of the spores to adverse environmental conditions. Dityrosine in vivo exists in both the LL and DL configurations and is part of an insoluble macromolecule of unknown structure. Here we present data indicating that dityrosine of the yeast spore wall is biosynthesized by a different mechanism than dityrosine in other biological systems--e.g., the hard fertilization membrane of the sea urchin egg. We identified two soluble, low molecular weight LL-dityrosine-containing spore wall precursors in extracts of sporulating cells and one precursor containing L-tyrosine. By expression of the previously described sporulation-specific genes DIT1 and DIT2 in vegetative cells, it was shown that DIT1 catalyzes the reaction leading from L-tyrosine to the tyrosine-containing precursor. DIT2, which is a member of the cytochrome P450 superfamily, is responsible for the dimerization reaction leading to the dityrosine-containing precursors. Epimerization of LL- to DL-dityrosine is one of the latest steps in spore wall formation and takes place after the dityrosine-containing precursors are incorporated into the spore wall. On the basis of these findings we suggest a biosynthetic pathway for the top layer of the yeast spore wall.

Four recombinant isoforms of Cor a I, the major allergen of hazel pollen, show different IgE-binding properties

Previous studies showed that pollens from trees of the order Fagales (e.g. birch, alder, hazel and hornbeam) all contain one major allergen. These proteins are cross-reactive between these tree species, and approximately 95% of tree-pollen-allergic patients display IgE binding to these allergens. Using the reported N-terminal amino acid sequence of the hazel pollen allergen Cor a I, it was possible to amplify Cor-a-I cDNA by use of the polymerase chain reaction. Four clones with cDNA inserts were isolated. All four clones contained an open reading frame of 477 nucleotides (159 amino acids) but differed in length of their 3'-non-coding regions. Within the overlapping regions, the nucleotide sequence of the 3'-non-coding regions of the four clones were nearly identical. The open reading frames coded for different isoforms of the major hazel pollen allergen, Cor a I. The clones were designated Cor a I/5, 6, 11 and 16, respectively. Comparison of the deduced amino acid sequences of these Cor a I isoforms revealed identities of 96-99%. The sequence identities between the Cor a I isoforms and Bet v I, the major birch pollen allergen, were 71-73% (80.5-83% similarity). Comparing amino acid sequences of Cor a I isoforms with the published sequences of Aln g I, the major allergen from alder, and Car b I and isoforms, the major allergen from hornbeam, 75.5-76.7% identity (83.6-85% similarity) and 83.6-89.9% sequence identity (89.3-95% similarity), respectively, was found. The four Cor a I cDNAs were subcloned into plasmid pKK223-3 and expressed in Escherichia coli as non-fusion proteins; their capacity to bind serum IgE from tree-pollen-allergic patients was investigated. The four cloned isoforms showed an apparent molecular mass of 17 kDa in SDS/PAGE, identical to the natural, pollen-derived Cor a I. IgE antibodies from tree-pollen-allergic patients reacted with all four recombinant isoforms. However, we noted marked differences in the IgE-binding patterns of the distinct isoforms. Furthermore, Cor a I/11 was the only isoform recognized by the anti-(Bet v I) mAb, BIP 1. Our results demonstrate that Cor a I isoforms display different antigenic and allergenic properties, very likely due to few but significant changes in their amino acid sequences. These findings have implications for the development of reagents for diagnosis and immunotherapy of type I allergies.

DIT101 (CSD2, CAL1), a cell cycle-regulated yeast gene required for synthesis of chitin in cell walls and chitosan in spore walls

A mutant screen has been designed to isolate mutants in Saccharomyces cerevisiae deficient in spore wall dityrosine. As shown by electron microscopy, most of the mutant spores lacked only the outermost, dityrosine-rich layer of the spore wall. Mutant dit101, however, was additionally lacking the chitosan layer of the spore wall. Chemical measurements showed that this mutant does not synthesize chitosan during sporulation. The mutant spores were viable but sensitive to lytic enzymes (glusulase or zymolyase). Unlike most of the dit-mutants, dit101 did show a distinctive phenotype in vegetative cells: they grew normally but contained very little chitin and were therefore resistant to the toxic chitin-binding dye, Calcofluor White. The cells showed barely detectable staining of the walls with Calcofluor White or primulin. The decrease in the amount of chitin in vegetative cells and the absence of chitosan in spores suggested that the mutant dit101 could be defective in a chitin synthase. Indeed, a genomic yeast clone harboring the gene, CSD2, sharing significant sequence similarity with yeast chitin synthases I and II (C. E. Bulawa (1992), Mol. Cell. Biol. 12, 1764-1776), complemented our mutant and was shown to correspond to the chromosomal locus of dit101. Thus, the mutations dit101 and csd2 (and probably also call; M. H. Valdivieso et al., (1991), J. Cell Biol. 114, 101-109) were shown to be allelic. The gene was mapped to chromosome II and was located about 3 kb distal of GAL1. Using this DNA clone, a transcript of about 3500-4000 nucleotides was detected. Comparing RNA isolated from vegetative cells and from sporulating cells at different times throughout the sporulation process, no significant differences in DIT101 transcript levels could be detected indicating absence of sporulation-specific transcriptional regulation. However, the amount of DIT101 transcript changed significantly at different stages of the mitotic cell cycle, peaking after septum formation, but before cytokinesis. As most of the chitin synthesis of vegetative cells occurs at this stage of the cell division cycle, chitin synthesis mediated by DIT101 could be primarily regulated at the level of transcription in vegetatively growing cells.

Complementary DNA cloning and expression in Escherichia coli of Aln g I, the major allergen in pollen of alder (Alnus glutinosa)

Previous data showed that the major pollen allergens from trees of the order Fagales, in particular alder, birch, hazel, and hornbeam, are highly interrelated. As only the complete amino acid sequence of Bet v I, the major allergen from birch, has been known, it was of interest to obtain the primary structure of other major allergens of this group, to attribute IgE-binding properties to certain features of the amino acid sequences of those allergens. cDNA was synthesized from alder pollen mRNA, sequence-specifically amplified by polymerase chain reaction and cloned into plasmid bluescript. Comparison of the deduced amino acid sequences of Aln g I and Bet v I revealed a 86.8% homology. The Aln g I encoding cDNA was subcloned into pKK223-3 and expressed in Escherichia coli as a full-length nonfusion protein. The recombinant Aln g I bound IgE from tree pollen-allergic patients and was shown to share IgE-epitopes with Bet v I by inhibition studies with recombinant Bet v I. Computer-aided calculations predicted epitopes in both Aln g I and Bet v I at the same position; the Bet v I molecule was predicted to possess two additional epitopes near the N-terminus of the molecule.

Determination of D-alanine and D-glutamic acid in biological samples by coupled-column chromatography using beta-cyclodextrin as mobile phase additive

A high-performance liquid chromatographic assay for monitoring traces of D-alanine and D-glutamic acid in peptide and protein hydrolysates is presented, which uses a two-column set-up with column switching. The main advantage of the proposed method is the higher reliability of the results, compared with the analysis by derivatization and single-column chromatography of the diastereomers. A non-chiral alkyl-silica reversed-phase column is combined with a second column, in which beta-cyclodextrin is used as a chiral mobile phase additive. The amino acids of the hydrolysate are dansylated, and the amino acid of interest is separated from the others on the first column and transferred to the second column where chiral resolution is performed. The transfer volume of ca. 200 microliters is small enough not to cause any peak distortion or dilation in the second column.

Distribution of allergens and allergen-coding mRNAs in various tissues of white birch

The distribution of allergenic proteins was investigated in various tissues of white birch, Betula verrucosa (pollen, leaves and male inflorescences containing immature pollen). In addition, callus and suspension culture cells were investigated for expression of IgE-binding proteins. Furthermore, RNA was extracted from all these tissues and subjected to in vitro translation in a cell-free wheat germ system. Bet v I, the major birch pollen allergen, could be extracted easily from pollen, and in low amounts from callus and leaves. No Bet v I could be extracted from immature male inflorescences. Minor allergens were expressed in high concentrations in pollen and in low concentrations in immature male inflorescences. No minor allergens could be detected in callus and leaves. In contrast to these observations, RNA from all the tissues as well as from callus could be translated in vitro into Bet v I as well as into minor allergens, in particular birch profilin (Bet v II), an important minor allergen. These data suggest that IgE-binding proteins of B. verrucosa, especially Bet v I, under certain circumstances can readily be synthesized in tissues other than pollen. This concept is corroborated by the recent observation that Bet v I reveals high homology with disease resistance response gene products from other plants, suggesting a similar function of Bet v I for the birch.

Recombinant allergens for immunoblot diagnosis of tree-pollen allergy

Diagnosis of type I allergy essentially depends on the availability of defined allergens, which can be provided by recombinant deoxyribonucleic acid (DNA) technology. We have previously isolated the c(complementary)DNAs encoding the major birch-pollen allergen, Bet v I, and another allergen with a molecular weight of 14 kd that was identified as birch profilin and designated Bet v II. These cDNAs were isolated from a lambda gt11 expression library by screening with the serum IgE from allergic patients. To obtain expression in Escherichia coli of recombinant allergens without additional fused polypeptides, both cDNAs were inserted into the plasmid pKK223-3. E. coli cells expressing Bet v I and birch profilin (Bet v II) were used for the preparation of recombinant proteins. These proteins were tested for their IgE-binding properties on immunoblots with sera from 100 different birch pollen-allergic patients. All patients' sera, which reacted with the natural allergens, Bet v I and Bet v II, demonstrated an identical IgE-binding pattern to recombinant birch-pollen allergens. Recombinant allergens may therefore be useful for the setup of diagnostic tests that allow the discrimination of different IgE-binding patterns as well as for patient-tailored immunotherapy.

Common epitopes of birch pollen and apples--studies by western and northern blot

Eighty-three sera from patients with birch-pollen allergy were investigated for IgE antibodies against apple allergens by means of immunoblotting. In immunoblots, 81 patients (97.6%) exhibited IgE directed against the major allergen of birch, Bet v I (17 kd), and these patients also demonstrated IgE binding to apple allergens in the molecular weight range 17 to 18 kd. Inhibition studies by preincubation of sera with birch-pollen extract led to complete blocking of IgE binding to this 17 to 18 kd protein, whereas preincubation with apple extract could not diminish IgE binding to Bet V I. Furthermore, a 17 kd protein in apple extract could be detected by immunoblotting with a Bet v I-specific monoclonal antibody. Northern blotting with a Bet v I cDNA clone as a probe revealed cross-hybridization of birch and apple allergen coding nucleic acids under conditions of high stringency, suggesting significant homology of the nucleic acid level. Our results support the concept that antigens in birch pollen and apples share allergenic epitopes leading to IgE cross-reactivities that may cause clinical manifestations when a special threshold level of specific IgE antibodies is reached.

Identification of profilin as a novel pollen allergen; IgE autoreactivity in sensitized individuals

A complementary DNA encoding a pollen allergen from white birch (Betula verrucosa) that was isolated from a pollen complementary DNA library with serum immunoglobulin E from a birch pollen-allergic individual revealed significant sequence homology to profilins. The recombinant protein showed high affinity to poly-L-proline. Immunoglobulin E antibodies from allergic individuals bound to natural and recombinant birch profilin and also to human profilin. In addition, birch and human profilin induced histamine release from blood basophils of profilin-allergic individuals, but not of individuals sensitized to other plant allergens. The structural similarity of conserved proteins might therefore be responsible for maintaining immunoglobulin E antibody titers in type I allergy.

The immunological relationship of epitopes on major tree pollen allergens

The major allergens of birch (Bet v I), alder (Aln g I), hazel (Cor a I) and hornbeam (Car b I) were investigated by means of high-resolution two-dimensional electrophoresis combined with immunoblotting. Eleven sera derived from patients allergic to birch pollen as well as mouse monoclonal antibodies BIP 1 and BIP 4, raised against Bet v I, were used as probes. Human IgE antibodies detected 10 spots in birch (Mr 17 kDa, pI 4.9-5.9); four spots in alder (Mr 18.5 kDa, pI 4.7-5.3); four spots in hazel (Mr 17 kDa, pI 5.0-5.8); and 12 + 7 spots in hornbeam (Mr 16.5 kDa, pI 4.9-6.6 and Mr 18 kDa, pI 5.2-6.7), respectively, representing major allergens. Each patient tested reacted in a similar fashion with the spot cluster(s) of a certain allergen. BIP 1 detected the same spot clusters as patients' IgE. BIP 4 reacted with the 17-, 18.5- and 18-kDa spots of birch, alder and hornbeam, but did not react with the 17-kDa spots of hazel and the 16.5-kDa spots of hornbeam. In inhibition experiments with birch pollen extract as inhibitor, IgE binding to Bet v I, as well as to Aln g I, Cor a I and Car b I was abolished, thus suggesting that IgE binding to major tree pollen allergens is confined to shared epitopes. These findings indicate that it might be sufficient to use only Bet v I for diagnostic procedures as well as for immunotherapy in patients with tree pollen allergy.

Homology of the major birch-pollen allergen, Bet v I, with the major pollen allergens of alder, hazel, and hornbeam at the nucleic acid level as determined by cross-hybridization

To investigate the relationship of the major allergens of birch (Bet v I), alder (Aln g I), hazel (Cor a I), and hornbeam (Car b I) at the nucleic acid level, a cDNA clone coding for the complete Bet v I protein was used for Northern and Southern blot experiments. RNAs were isolated from pollen of birch (Betula verrucosa), alder (Alnus glutinosa), hazel (Corylus avellana), and hornbeam (Carpinus betulus). Hybridization was performed at different stringencies. At high stringency, comparable binding of the complete Bet v I cDNA probe to pollen RNAs from birch, alder, and hazel could be observed, indicating high homology of the mRNAs coding for these allergens. With the 3' and 5' half fragments of the Bet v I cDNA, both probes bound to transcripts of all four tree pollens, but most strongly to birch RNA. In Southern blots, distinct binding patterns of genomic DNA digests of birch, alder, hazel, and hornbeam were observed. Most bands were observed with birch DNA digests and less with alder, whereas in genomic DNA digests of hornbeam and hazel, only one band was observed. The result of these cross-hybridization experiments indicate a high homology at the nucleic acid level of the four major allergens of trees belonging to the order Fagales. The sequence similarity presented here further corroborates earlier observations of immunologic cross-reactivity at the protein level. Therefore, in the case of the major allergens of the Betulaceae, an extract with only one major allergen, preferentially Bet v I, instead of all four major allergens, should be sufficient for diagnostic and therapeutic purposes.

Allergen profiles of dog hair and dander, body fluids and tissues as defined by immunoblotting

The sera from 25 patients with clinical type I allergy against dogs were investigated by means of immunoblotting, using extracts of dog hair/dander, skin, hair, saliva, salivary gland, serum and liver. 96% of the patients' sera showed IgE antibodies reactive with 19- and 23-kilodalton (kDa) proteins in the hair/dander extract. The 23-kDa IgE-binding protein was preferentially detected in the hair extract and saliva but not in skin, salivary gland, serum and liver extracts. The 19-kDa band was strongly expressed in skin, but not in hair, serum and liver. Inhibition experiments using the 23-kDa containing extract prepared from hair and the 19-kDa containing extract prepared from skin revealed that these two proteins are likely to be immunologically independent allergens.

A low molecular weight allergen of white birch (Betula verrucosa) is highly homologous to human profilin

Cloning of allergens has contributed substantially to the understanding of mechanisms in allergic diseases by providing information about the sequence and hence biological functions of allergens. The major birch pollen allergen, Bet v I [Breiteneder H, et al: EMBO J 1989;8:1935-1938] and the white-faced hornet venom allergen (antigen 5) [Si Yun Fang K, et al: Proc. Natl. Acad. Sc. USA 1988;85:895-899] were shown to be highly homologous to pathogenesis-related proteins of plants. In the case of the major allergen of house dust mite, Der p I, homology to proteases was demonstrated. Therefore, the proposed biological function of these IgE-binding proteins might be related to their allergenic potential. In this paper we tentatively identify a ubiquitous family of low molecular weight allergens as profilins. The identification is based on a sequence homology, (b) binding to poly(L-proline), and (c) immunological cross-reactivity. Recombinant birch profilin was purified to homogeneity and showed the same properties as natural profilins.

Isolation of two developmentally regulated genes involved in spore wall maturation in Saccharomyces cerevisiae

During sporulation of Saccharomyces cerevisiae, the four haploid nuclei generated by meiosis are encapsulated within multilayered spore walls. Taking advantage of the natural fluorescence imparted to yeast spores by the presence of a dityrosine-containing macromolecule in the spore wall, we identified and cloned two genes, termed DIT1 and DIT2, which are required for spore wall maturation. Mutation of these genes has no effect on the efficiency of spore formation or spore viability. The mutant spores, however, fail to accumulate the spore wall-specific dityrosine and lack the outermost layer of the spore wall. The absence of this cross-linked surface layer reduces the resistance of the spores to lytic enzymes, to ether, and to elevated temperature. Expression of the DIT and DIT2 genes is restricted to sporulating cells, with the DIT1 transcripts accumulating at the time of prospore enclosure and just prior to the time of dityrosine biosynthesis. Both genes act in a spore-autonomous manner implying that at least some of the activities responsible for forming the outermost layer of the spore wall reside within the developing spore rather than in the surrounding ascal cytoplasm. As the DIT2 gene product has significant homology with cytochrome P-450s, DIT2 may be responsible for catalyzing the oxidation of tyrosine residues in the formation of dityrosine.

Characterization of a DL-dityrosine-containing macromolecule from yeast ascospore walls

We have shown previously that the outer layers of yeast ascospore walls contain dityrosine and that this amino acid is a major component of the cross-linked peptides present in the spore wall (Briza, P., Winkler, G., Kalchhauser, H., and Breitenbach, M. (1986) J. Biol. Chem. 261, 4288-4294). We now present evidence that dityrosine is located in the outermost layer and that it is in the DL-configuration. Although the proteins (peptides) of the spore wall are insoluble, the macromolecule containing dityrosine can be solubilized by partial acid hydrolysis of spore walls. Analysis of this macromolecule indicates that it contains more than 50 mol% dityrosine and a very limited number of other amino acids. Interestingly, part of the dityrosine of spore walls is present in the DL-configuration. We speculate that not only the high degree of cross-links in the outermost layer but also the D-configuration of part of the alpha-C-atoms of dityrosine could contribute to the spores' resistance to lytic enzymes.

Evaluation of immunotherapy-induced changes in specific IgE, IgG and IgG subclasses in birch pollen allergic patients by means of immunoblotting. Correlation with clinical response

Sera from 27 birch pollen-allergic patients who had undergone hyposensitization treatment for 22-41 months were studied by immunoblotting before and after therapy, whereby the levels of IgE, IgG and IgG1-4 antibodies directed against the major allergen Bet v I and minor allergens of birch pollen were monitored. The clinical benefit of immunotherapy (IT) was evaluated using a symptom specific questionnaire. In patients with good clinical response (responders, n = 18), as defined by improvement of symptoms, anti-Bet v I IgE antibodies were found to decrease in 10/18 patients (55.5%), whereas in 6/18 (33.3%) no change and in two cases (11.2%) an increase of specific IgE was observed. In the group of patients with unsatisfactory clinical outcome (non-responders, n = 9), 3/9 patients (33.3%) showed a decrease, 3/9 (33.3%) no change and 3/9 (33.3%) an increase in levels of IgE antibodies directed against Bet v I. In the case of minor allergens, 5/18 responders (27.7%) and 8/9 non-responders (88.8%) showed specific IgE before IT. In the responder group, no increase of specific IgE could be observed after IT. In non-responders, however, an increase of IgE directed against minor allergens was seen in 3/9 patients (33.3%). In all patients, regardless of therapeutical success, IT-induced elevated levels of specific IgG, IgG1 and in particular IgG4 directed against Bet v I were found. Regarding minor allergens, a heterogeneous pattern of IgG responses without significant correlation to clinical benefit was observed. Our results indicate that changes in IgG reactivity patterns against Bet v I and minor allergens, as shown by the immunoblot technique, did not correlate with good or bad clinical outcome.

[What is the contribution of yeast genetics to tumor biology and tumor diagnosis?]

This short review article discusses methods and results of oncogene research in yeast. Current knowledge of the sequence, expression and biological function of ras-homologous genes of the yeast Saccharomyces cerevisiae is presented, as well as the implications of these findings for oncogene research in mammals. We review recent examples of highly conserved eukaryotic genes involved in growth control and mitosis control, including recent work from our own laboratories.

IgE and IgG antibodies of patients with allergy to birch pollen as tools to define the allergen profile of Betula verrucosa

IgE and IgG antibody response to birch pollen antigens were studied by means of immunoblotting experiments testing 58 sera from patients with Type I allergy to birch pollen. 56/58 patients showed IgE antibodies reactive with Bet v I, a 17 kilodalton (kD) pollen protein. 2D-electrophoresis/immunoblot revealed a heterogeneity of that protein. Ten spots (pH 4.9-5.9) could be detected, presumably representing differentially glycosylated isoallergens. In 33/58 patients, there was no evidence of IgE antibodies directed against allergens other than Bet v I. However, in 25/58 of patients' sera, 11 minor allergens (13, 15, 18, 27, 29, 32, 39, 44, 57, and 68 kD) with individual incidences from 1.7% to 17.2% were identified. All proteins were also recognized by the patients' IgG antibodies: in the case of Bet v I recognition was weak, whereas the IgG response to the minor allergens was pronounced. Sera from healthy individuals showed similar IgG antibody responses, but no IgG to the 15, 27, and 29 kD proteins. Our results suggest that IgG directed against minor allergens may function as trapping antibodies in healthy individuals. Too low or lacking amounts of anti-Bet v I IgG may facilitate an allergic reaction.

The gene coding for the major birch pollen allergen Betv1, is highly homologous to a pea disease resistance response gene

Pollen of the white birch (Betula verrucosa) is one of the main causes of Type I allergic reactions (allergic rhinoconjunctivitis, allergic bronchial asthma) in Middle and Northern Europe, North America and the USSR. Type I allergies are a major threat to public health in these countries, since 10-15% of the population suffer from these diseases. BetvI, an allergenic protein with an Mr of 17 kd is a constituent of the pollen of white birch and is responsible for IgE binding in more than 95% of birch pollen allergic patients. Here, we report the complete nucleotide sequence and deduced amino acid sequence of a cDNA clone coding for the major pollen allergen (BetvI) of white birch. It is similar to the N-terminal peptide sequences of the allergens of hazel, alder and hornbeam (close relatives) but it has no significant sequence homology to any other known allergens. However, it shows 55% sequence identity with a pea disease resistance response gene, indicating that BetvI may be involved in pathogen resistance of pollen.

[IgE and IgG antibody response in patients with type I allergy to birch pollen]

IgE and IgG antibody responses to birch pollen were investigated in sera derived from patients with type I allergy to birch pollen by means of immunoblotting. 56/58 patient sera contained IgE antibodies to a 17 kD pollen protein, recently designated as Bet v 1. In 33/58 patient sera no evidence was obtained for IgE antibodies to other pollen proteins than Bet v 1. However, in 25/58 sera, IgE antibodies reacting with 11 different allergens of 13, 15, 18, 27, 29, 32, 36, 39, 44, 57, 68 kD with an individual prevalence ranging from 1.7% to 17.2% were identified. All these IgE-binding proteins were also recognized by patients IgG. IgG responses to Bet v 1 were rather weak or lacking entirely, whereas in the case of the minor allergens pronounced IgG responses were observed. Samples from patients undergoing hyposensitization therapy showed an induction of anti-Bet v 1 IgG and a decrease in anti-Bet v 1 IgE upon treatment. These changes in antibody profiles to Bet v 1 did not correlate with the clinical benefit of the hyposensitization therapy.

Monoclonal antibodies against birch pollen allergens: characterization by immunoblotting and use for single-step affinity purification of the major allergen Bet v I

Two monoclonal antibodies against birch pollen proteins were produced by immunizing BALB/c mice with birch pollen extract. In immunoblotting experiments, antibody BIP 1 reacted with a 17-kilodalton (kD) protein considered to represent the major birch pollen allergen Bet v I. A second monoclonal antibody, BIP 3, reacted with 3 different birch pollen proteins of molecular weights 32, 36 and 68 kD of which the 36- and 68-kD proteins corresponded to minor allergens of birch pollen. Two-dimensional electrophoresis/immunoblotting experiments revealed that BIP 1 reacted with all Bet v I isoallergens, also identified by human IgE antibodies. Using BIP 1 coupled to Sepharose 4B as reverse immunosorbent, Bet v I was obtained in a single-step procedure and characterized as single band by SDS-PAGE.

Chemical composition of the yeast ascospore wall. The second outer layer consists of chitosan

In a preceding paper (Briza, P., Winkler, G., Kalchhauser, H., and Breitenbach, M. (1986) J. Biol. Chem. 261, 4288-4294), we reported the presence of dityrosine in the outer layers of yeast ascospore walls. Both outer layers seen in electron micrographs of yeast ascospore walls are sporulation-specific. Here we show that the second of these two outer layers consists of chitosan. In intact spores, it is shielded from staining with primulin by the outermost layer. However, in purified spore walls, the second layer is brightly stained by primulin, and hydrolysates of such preparations contain about 10% glucosamine relative to spore wall dry weight. The spore wall material staining with primulin is resistant to chitinase, but readily degraded by treatment with HNO2. Acetylation prior to HNO2 treatment completely prevents its degradation. A partial acid hydrolysate of spore walls contains predominantly soluble poly-beta-(1,4)-glucosamine as determined by 13C NMR spectroscopy. By these criteria, the glucosamine polymer of yeast ascospore walls is chitosan. As spore walls treated with alkali lack the inner layers but contain chitosan and as chitosan is not exposed at the surface of the spore, we conclude that it is localized in the second outer layer of the spore wall.

Isolation and characterization of messenger RNA from male inflorescences and pollen of the white birch (Betula verrucosa)

A glycoprotein with a molecular weight (MW) of 17 kilodaltons (kD), Bet v I, represents the major allergen of the white birch (Betula verrucosa, BV) and plays an important role in tree-pollen-induced type I allergic reactions. In order to characterize the major and also some minor allergens of BV, we investigated the IgE-binding properties of these allergens using immunoblot techniques. Normal and patients' sera were employed for this study. Furthermore, RNA from male inflorescences and from pollen of BV were isolated and purified by affinity chromatography on oligo-dT-cellulose. Poly(A)+-mRNA thus obtained was translated in vitro in a cell-free wheat germ system and the proteins synthesized were separated by SDS-PAGE and transferred to nitrocellulose. The blots were incubated with normal human sera and with sera from patients allergic to birch pollen. Bound IgE antibodies were detected with 125I-labeled anti-IgE. We observed major IgE binding to a protein of an MW of 12.5 kD, and little IgE binding to a 17-kD protein, presumably Bet v I. Comparing the products of in vitro translation from mRNA preparations of mature pollen and of male inflorescences collected in June, October and February, little seasonal variations could be observed. As the in vitro translation system does not glycosylate proteins, our results show that the majority of IgE in patients' sera is not directed against the carbohydrate moieties of these allergens.

Dityrosine is a prominent component of the yeast ascospore wall. A proof of its structure

The yeast ascospore wall consists of four morphologically distinct layers. The hydrophobic surface layers are biogenically derived from the prospore wall and appear dark after OsO4 staining. They seem to be responsible for the stability of the spores against attack by lytic enzymes. By amino acid analysis of acid hydrolysates of ascospore walls, two new peaks were detected, which were shown to be the racemic and meso form, respectively, of dityrosine. The identity of this hitherto unknown component of the yeast ascospore wall with standard dityrosine was proven by 1H NMR and by mass spectrometry. A 13C NMR spectroscopic investigation of the structure of dityrosine confirmed that, in natural dityrosine, the biphenyl linkage is located ortho, ortho to the hydroxyl groups. Following digestion of the inner layers of isolated ascospore walls it was shown that dityrosine is very probably located only in the surface layers. The same conclusion was reached independently by an investigation of spores of a strain homozygous for the mutation gcn1, which lack the outermost layers of the spore wall and were practically devoid of dityrosine. In sporulating yeast, L-tyrosine was readily incorporated into the dityrosine of the ascospore wall. Control experiments involving vegetative a/alpha cells and nonsporulating alpha/alpha cells under sporulation conditions showed that dityrosine is indeed sporulation-specific.

RAS2 of Saccharomyces cerevisiae is required for gluconeogenic growth and proper response to nutrient limitation

Saccharomyces cerevisiae contains two genes with remarkable homology to members of the ras oncogene family. These two genes, RAS1 and RAS2, constitute an essential gene family since spores with disruptions of both genes fail to grow. We report here that strains containing RAS2 disruptions have three distinct phenotypes. First, they fail to grow efficiently on nonfermentable carbon sources. Second, they hyperaccumulate the storage carbohydrates glycogen and trehalose. Third, diploid cells homozygous for the RAS2 disruptions sporulate on rich media. Extragenic suppressors have been isolated that suppress the gluconeogenic defect. These suppressors fall into at least three complementation groups, mutations in two of which bypass the normal requirement of RAS for cell viability, allowing cells containing neither RAS gene to grow. The phenotype of the RAS2 mutant and extragenic suppressors implicate RAS with some function in the normal response to nutrient limitation.

Mitochondrial circular RNAs are absent in sporulating cells of Saccharomyces cerevisiae

During sporulation of Saccharomyces cerevisiae the mitochondria undergo a differentiation process, leading to a "spore mitochondrion", which differs both physiologically and morphologically from vegetative cell mitochondria. We report here the behaviour of the mitochondrial transcripts during this differentiation process. The circular transcripts representing spliced introns of the two mitochondrial split genes for cytochrome b and for the subunit 1 of the cytochrome c oxidase, which are very abundant during vegetative growth, are not detectable in sporulating cells. This loss does neither take place in haploid cells under sporulation conditions nor when erythromycin is added to the medium. The process of some mRNAs is advanced in relation to their precursors in sporulating cells.

Metabolism of myo-inositol during sporulation of myo-inositol-requiring Saccharomyces cerevisiae

We investigated the sporulation properties of a series of diploid Saccharomyces cerevisiae strains homozygous for inositol auxotrophic markers. The strains required different amounts of inositol for the completion of sporulation. Shift experiments revealed two phases of inositol requirement during sporulation which coincided with the two phases of lipid synthesis found by earlier workers. Phase I was at the beginning and during premeiotic deoxyribonucleic acid synthesis; phase II immediately preceded the appearance of mature asci. Of the inositol taken up by sporulating cells, 90% was incorporated into inositol phospholipids. By two-dimensional thin-layer chromatography, eight compounds were resolved, one of which was sporulation specific. The majority of the inositol phospholipids were, however, identical to those found in vegetatively growing cells. In the absence of inositol, the cells did not sporulate but, after a certain time, were unable to return to vegetative growth. These nonsporulating cells did, however, incorporate acetate into lipids and double their deoxyribonucleic acid content in the premeiotic phase. We believe that it is this lack of coordination of biosynthetic events which causes inositol-less death on sporulation media without inositol.

Mithramycin and DIPI: a pair of fluorochromes specific for GC-and AT-rich DNA respectively

The AT specificity of the fluorochromes DIPI and DAPI and the GC specificity of mithramycin are evidenced by observations in human, mouse, and bovine chromosomes. DIPI and DAPI produce a pattern similar to Hoechst 33258 in all three species, whereas mithramycin results in a reverse pattern. The AT-rich centromeric heterochromatin in mouse is brilliantly stained by DIPI or DAPI and remains nearly invisible after mithramycin staining. In the GC-rich centromeric heterochromatin of cattle the opposite behavior is observed.

DIPI and DAPI: fluorescence banding with only negliglible fading

DIPI and DAPI produce distinct fluorescent bands in human chromosomes similar to quinacrine banding patterns. Additionally, the AT rich secondary constrictions in the chromosomes Nos. 1, 9 and 16 are brightly fluorescent. On the other hand the brilliantly fluorescent regions after staining with quinacrine mustard in the chromosomes Nos. 3 and 4, satellites and some other regions in the acrocentric chromosomes are less striking. The distal part of the Y, however, is clearly discernible. Thus DIPI and DAPI seem to be strictly AT specific fluorochromes like Hoechst 33258. In interphase nuclei the Y chromosome can be identified. However, quinacrines are superior for Y-body analysis in buccal, hair cell and sperm smears. BrdU labeled chromatids show reduced fluorescence intensity. The difference, however, is less apparent than after staining with Hoechst 33 258. DAPI and especially DIPI are highly resistant to UV-irradiation; there is almost no fading within 30 min when using DIPI. Moreover, fluorescence intensity is stronger than in quinicrines. When photographing, exposure times may be reduced to about one quarter compared to quinacrine mustard.