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PubMed1993

Signal transduction during mating and meiosis in S. pombe.

When starved, the fission yeast Schizosaccharomyces pombe responds by producing mating factors or pheromones that signal to cells of the opposite sex to initiate mating. Like its distant relative Saccharomyces cerevisiae, cells of the two mating types of S. pombe each produce a distinct pheromone that binds to receptors on the opposite cell type to induce the morphological changes required for mating. While the pathways are basically very similar in the two yeasts, pheromone signalling in S. pombe differs in several important ways from that of the more familiar budding yeast. In this article, Olaf Nielsen describes the pheromones and their effects in S. pombe, and compares the signalling pathways of the two yeasts.

Journal Article↗
PubMed1997

A murine model of factor XI deficiency.

To facilitate investigations into the physiologic and pathologic roles of factor XI, we have developed a murine model of severe factor XI deficiency using the technique of homologous recombination in embryonic stem cells. The factor XI gene was disrupted by introducing a neomycin phosphotransferase gene into the fifth exon. The activated partial thromboplastin times of homozygous null mice were prolonged (158- > 200 s) compared with wild type (25-34 s) and heterozygous null (40-61 s) litter mates. Factor XI activity was absent from the plasma of mice homozygous for the null mutation and factor XI mRNA was undetectable by Northern blot and reverse transcription/PCR in the livers of homozygous null animals. The genotypes of progeny from matings of mice heterozygous for the factor XI null allele followed the expected Mendelian ratio (1:2:1, wild type 26%, heterozygote null 54%, homozygous null 20%), indicating that severe factor XI deficiency did not result in increased intrauterine death. Results of a tail transection bleeding time assay were similar for wild type and homozygous null animals with, at most, a tendency for slightly prolonged bleeding in the homozygous null animals. The factor XI deficient mice are a unique tool for evaluating the role of factor XI in normal hemostasis and pathologic coagulation.

Animals↗
PubMed1996

Mutations within the first LSGGQ motif of Ste6p cause defects in a-factor transport and mating in Saccharomyces cerevisiae.

Mating between the two haploid cell types (a and alpha) of the yeast Saccharomyces cerevisiae depends upon the efficient secretion and delivery of the a- and alpha-factor pheromones to their respective target cells. However, a quantitative correlation between the level of transported a-factor and mating efficiency has never been determined. a-Factor is transported by Ste6p, a member of the ATP-binding cassette (ABC) family of transporter proteins. In this study, several missense mutations were introduced in or near the conserved LSGGQ motif within the first nucleotide-binding domain of Ste6p. Quantitation of extracellular a-factor levels indicated that these mutations caused a broad range of a-factor transport defects, and those directly within the LSGGQ motif caused the most severe defects. Overall, we observed a strong correlation between the level of transported a-factor and the mating efficiency of these strains, consistent with the role of Ste6p as the a-factor transporter. The LSGGQ mutations did not cause either a significant alteration in the steady-state level of Ste6p or a detectable change in its subcellular localization. Thus, it appears that these mutations interfere with the ability of Ste6p to transport a-factor out of the MATa cell. The possible involvement of the LSGGQ motif in transporter function is consistent with the strong conservation of this sequence motif throughout the ABC transporter superfamily.

ATP-Binding Cassette Transporters↗
PubMed2000

The effect of ecological factors on the mating system of a South American shrub species (Helicteres brevispira).

Mating systems are influenced by several ecological factors, including plant density, number of flowers per plant, and pollinator movements. In this study, we investigated the simultaneous effects of these three factors on the mating system of a self-compatible Brazilian shrub species: Helicteres brevispira St. Hil. Outcrossing rate is directly correlated with plant density. Changes in the number of flowers per plant affect outcrossing rate through their effect on the density of flowers. Variation in foraging behaviour of hummingbird pollinators is a consequence of the interaction between plant density and number of flowers per plant. Territorialist pollinators are common in high density areas but visit few flowers on each plant, thereby promoting outcrossing. In areas of low plant density, trapliners and rare territorialists visit several flowers per plant, thus increasing selfing. Our results indicate that outcrossing rate is a dynamic parameter, with the extent of variation depending on a number of ecological factors. In successional species such as those in the genus Helicteres, demographic changes may be accompanied by alterations in mating system parameters, with concomitant effects on the genetic structure of populations.

Crosses, Genetic↗
PubMed1992

The a mating type locus of U. maydis specifies cell signaling components.

The a mating type locus of the phytopathogenic fungus U. maydis controls fusion of haploid cells and filamentous growth of the dikaryotic mycelium. The a locus exists in two alleles, termed a1 and a2, which are defined by nonhomologous DNA regions comprising 4.5 kb for a1 and 8 kb for a2, flanked by identical sequences. Based on functional assays, mutants, and sequencing, we demonstrate that the mating type in each allele is determined by a set of two genes. One encodes a precursor for a lipopeptide mating factor, and the other specifies the receptor for the pheromone secreted by cells of opposite mating type. Thus, U. maydis employs a novel strategy to determine its mating type by providing the primary determinants of cell-cell recognition directly from the mating type locus.

Alleles↗
PubMedDate not supplied

Signal transduction in yeast mating: receptors, transcription factors, and the kinase connection.

In the yeast Saccharomyces cerevisiae, peptide mating pheromones activate a signal transduction pathway that leads to cellular differentiation and cell division cycle arrest. It is now possible to trace the major events of this pathway. binding of pheromone to G-protein-coupled receptors activates a cascade of serine/threonine protein kinases that ultimately phosphorylate and increase the activity of an identified transcription factor.

Cell Cycle↗
PubMed1997

Modulation of Ras and a-factor function by carboxyl-terminal proteolysis.

Prenylated proteins contain a covalently linked cholesterol intermediate near their carboxyl-termini. Maturation of most prenylated proteins involves proteolytic removal of the last three amino acids. Two genes in Saccharomyces cerevisiae, RCE1 and AFC1, were identified that appear to be responsible for this processing. The Afc1 protein is a zinc protease that participates in the processing of yeast a-factor mating pheromone. The Rce1 protein contributes to the processing of both Ras protein and a-factor. Deletion of both AFC1 and RCE1 resulted in the loss of proteolytic processing of prenylated proteins. Disruption of RCE1 led to defects in Ras localization and signaling and suppressed the activated phenotype associated with the allele RAS2val19.

Cell Membrane↗
PubMed2001

[High efficient expression of recombinant human platelet factor IV in Pichia pastoris].

OBJECTIVE: To express recombinant human platelet factor 4 (PF4) in methanol yeast. METHODS: PF4 cDNA amplified by PCR was cloned into the mating factor alpha (MFalpha) signal sequence, downstream the alcohol oxidase 1 (AOX 1) promoter of the pPIC9 vector. The reconstructed vector was subsequently integrated into the methanol yeast P. pastoris strain GS115. The highly expressing strain was selected and the protein sequences and their biological activities were assayed. RESULTS: The amino acid sequence of rhPF4 was the same as that of natural one. The rhPF4 can neutralize the anticoagulation effect of heparin in a dose-dependent manner. CONCLUSION: The amount of rhPF4 expressed in methanol yeast meets well the scale for manufacturing. The biological activities of the rhPF4 were the same as that of natural PF4.

Cloning, Molecular↗
PubMed1985

Synthesis and biological activity of N epsilon-acyl derivatives of a Saccharomyces cerevisiae mating pheromone.

We report a general method for acylation of the N epsilon-amino group of the lysyl residue in peptides. The procedure involves acylation using p-nitrophenyl esters and 1-hydroxybenzotriazole in organic solvents to yield a series of fatty acyl mating pheromones of Saccharomyces cerevisiae. The fatty acyl group does not influence coupling of peptide fragments. Biological activities of the synthesized alpha-factor mating pheromones derivatized with acetyl, butyryl, caprylyl and lauryl groups are nearly equivalent to the activity of unacylated alpha-factor. The N epsilon-stearyl-alpha-factor is biologically inactive. The procedures reported in this communication can be used to increase hydrophobicity of lysine-containing peptides when the lysyl group is not essential for activity.

Animals↗
PubMed1991

Efficient expression of bovine alpha-lactalbumin in Saccharomyces cerevisiae.

A synthetic gene encoding the mature bovine alpha-lactalbumin fused to the preproregion of the yeast alpha-mating factor has been expressed and secreted at high level in Saccharomyces cerevisiae under the control of the alpha-mating promoter. Growth conditions were found to be critical for the expression: recombinant alpha-lactalbumin could only be detected in the medium provided the culture was grown at neutral pH. The secreted bovine alpha-lactalbumin is enzymatically active and identical to the whey protein, as confirmed by SDS/PAGE, IEF, ultraviolet and CD spectral analysis, and amino-terminal sequence determination.

Amino Acid Sequence↗
PubMed2000

A temporal analysis of sexual activity in a natural population of Drosophila willistoni.

We have analyzed the mating activity of F1 flies in mating chamber from five samples of wild Drosophila willistoni females. The files were collected from an area (in south Brazil) that has well-defined seasons and considerable variation in temperature and in the abundance of drosophilids. We estimated copulation frequency at first five minutes of observation, copulation frequency at ninety minutes of observation and copulation latency. We did not observe differences in the total copulation frequency throughout seasons, as opposed to copulation frequency in the beginning of the observation period and to copulation latency which varied significantly. The results show that mating activity in a natural population can vary along with the seasons and that this variation can be correlated to some environmental factor. Mating activity tended to be higher during high warm temperature periods, when the flies were abundant.

Animals↗
PubMed2003

An EPR study of the secretion of G-CSF heterologous protein from Pichia pastoris.

The biologically active protein known as human granulocyte colony stimulating factor (G-CSF) can be efficiently secreted from the transformed GS115 Pichia pastoris (GS115/pPIC9/G-CSF), which contains an alpha-mating-factor prepro signal sequence and an alcohol oxidase I promoter, both introduced using the pPIC9 plasmid. To study the P. pastoris G-CSF protein-secretion process, changes to the plasma membrane's lateral domain structure were monitored using electron paramagnetic resonance (EPR). The GS115 and its transformed analogue show that the plasma membrane can be described by fluid-disordered and fluid-ordered lateral domains. The relative proportion of these domains is a sensitive parameter that is able to describe the membrane's involvement in the protein-excretion process. Here, P. pastoris GS115 served as a control for us to compare with the GS115/pPIC9/G-CSF heterologous protein-secreting cells. Electron paramagnetic resonance studies using the spin-probe 5-doxyl methyl ester of palmitic acid [MeFASL (10,3)] showed that during cultivation in a glycerol medium all types of cells had a relatively high proportion of cell-membrane fluid-disordered domains, while during the production phase the G-CSF protein-secreting cells showed a decrease in the proportion of fluid-disordered domains. We ascribe this effect to the vesicular lipid exchange caused by the fusion of secretary vesicles with the plasma membrane during exocytosis. Using electron microscopy and immunocytochemistry intracellular vesicles containing the G-CSF protein were detected. Our studies support the exocytotic mechanism of the heterologous protein secretion.

Cell Membrane Permeability↗
PubMed1997

Biogenesis of the Saccharomyces cerevisiae mating pheromone a-factor.

The Saccharomyces cerevisiae mating pheromone a-factor is a prenylated and carboxyl methylated extracellular peptide signaling molecule. Biogenesis of the a-factor precursor proceeds via a distinctive multistep pathway that involves COOH-terminal modification. NH2-terminal proteolysis, and a nonclassical export mechanism. In this study, we examine the formation and fate of a-factor biosynthetic intermediates to more precisely define the events that occur during a-factor biogenesis. We have identified four distinct a-factor biosynthetic intermediates (P0, P1, P2, and M) by metabolic labeling, immunoprecipitation, and SDS-PAGE. We determined the biochemical composition of each by defining their NH2-terminal amino acid and COOH-terminal modification status. Unexpectedly, we discovered that not one, but two NH2-terminal cleavage steps occur during the biogenesis of a-factor. In addition, we have shown that COOH-terminal prenylation is required for the NH2-terminal processing of a-factor and that all the prenylated a-factor intermediates (P1, P2, and M) are membrane bound, suggesting that many steps of a-factor biogenesis occur in association with membranes. We also observed that although the biogenesis of a-factor is a rapid process, it is inherently inefficient, perhaps reflecting the potential for regulation. Previous studies have identified gene products that participate in the COOH-terminal modification (Ram1p, Ram2p, Ste14p), NH2-terminal processing (Ste24p, Axl1p), and export (Ste6p) of a-factor. The intermediates defined in the present study are discussed in the context of these biogenesis components to formulate an overall model for the pathway of a-factor biogenesis.

Amino Acid Sequence↗
PubMed1993

Presence and biological activity of a GnRH-like factor in the nervous system of Helisoma trivolvis.

Gonadotropin-releasing hormone (GnRH) constitutes a family of neuropeptides found throughout the vertebrates. Although a GnRH-like peptide has also been isolated from yeast (alpha-mating factor), the presence of GnRH has not been clearly demonstrated in invertebrate phyla. In this study, we tested the hypothesis that GnRH-like peptides are present and functional in the central nervous system (CNS) of the gastropod mollusc, Helisoma trivolvis. The presence of a GnRH-like peptide was examined by three methods: (1) in immunofluorescence studies with four different antibodies generated against several GnRH peptides, select neurons and putative neurosecretory cells were specifically and consistently labelled throughout the CNS; (2) reverse-phase high performance liquid chromatography (HPLC) and radioimmunoassay (RIA) analysis revealed a GnRH-like factor which co-migrates with mammalian (m)GnRH; and (3) in bioactivity experiments, extracts of Helisoma trivolvis CNS mimicked GnRH in stimulating gonadotropin release from dispersed goldfish pituitary cells in static culture. Two functional assays were carried out to examine the potential biological roles of GnRH-like peptides in Helisoma. (1) Intracellular recordings of left-parietal and visceral ganglion neurons revealed diverse electrophysiological responses to mGnRH. These effects were attenuated by a mGnRH antagonist. (2) Addition of mGnRH arrested neurite outgrowth in a subpopulation of dissociated embryonic Helisoma neurons in culture. Taken together, these results strongly suggest that a mGnRH-like peptide is an important neuropeptide in Helisoma. A hypothesis is presented that GnRH-like peptides may be ancient factors that are conserved both structurally and functionally in the evolution of animals.

Animals↗
PubMed2002

Multiple functions of mfa-1, a putative pheromone precursor gene of Neurospora crassa.

A putative pheromone precursor gene of Neurospora crassa, mfa-1 (which encodes mating factor a-1), was identified as the most abundant clone in starved mycelial and perithecial cDNA libraries. Northern analysis demonstrated high mfa-1 expression in all mating type a tissues and suggested low expression levels in mat A tissues. The mfa-1 gene was expressed as an approximately 1.2-kb transcript predicted to encode a 24-residue peptide, followed by a long 3' untranslated region (3' UTR). The predicted MFA1 sequence showed 100% sequence identity to PPG2 of Sordaria macrospora and structural similarity (a carboxy-terminal CAAX motif) to many hydrophobic fungal pheromone precursors. Mutants with a disrupted open reading frame (ORF) in which the critical cysteine residue had been changed to a nonprenylatable residue, tyrosine (YAAX mutants), were isolated, as were mfa-1 mutants with intact ORFs but multiple mutations in the 3' noncoding region (CAAX mutants). The 3' UTR is required for the full range of mfa-1 gene activity. Both classes of mutants showed delayed and reduced vegetative growth (which was suppressed by supplementation with a minute amount [30 micro M] of ornithine, citrulline, or arginine), as well as aberrant sexual development. When crossed as female parents to wild-type males, the CAAX and YAAX mutants showed greatly reduced ascospore production. No ascospores were produced in homozygous mfa-1 crosses. As males, YAAX mat a mutants were unable to attract wild-type mat A trichogynes (female-specific hyphae) or to initiate sexual development, while CAAX mat a mutants were able to mate and produce sexual progeny despite their inability to attract mat A trichogynes. In the mat A background, both CAAX and YAAX mutants showed normal male fertility but defective vegetative growth and aberrant female sexual development. Thus, the mfa-1 gene appears to have multiple roles in N. crassa development: (i) it encodes a hydrophobic pheromone with a putative farnesylated and carboxymethylated C-terminal cysteine residue, required by mat a to attract trichogynes of mat A; (ii) it is involved in female sexual development and ascospore production in both mating types; and (iii) it functions in vegetative growth of both mating types.

3' Untranslated Regions↗
PubMed1998

Characterization of the microheterogeneities of PIXY321, a genetically engineered granulocyte-macrophage colony-stimulating factor/interleukin-3 fusion protein expressed in yeast.

PIXY321, a human cytokine analog genetically engineered by the fusion of granulocyte-macrophage colony-stimulating factor (GM-CSF) and interleukin-3 (IL-3), was expressed in yeast under the control of the alcohol dehydrogenase 2 (ADH2) promoter and the alpha-mating factor expression system. To provide the material necessary for the evaluation of PIXY321 in clinical trials, the production was scaled up to the 1200-1 scale and the PIXY321 molecule isolated by four successive steps of ion-exchange chromatography. Multiple heterogeneities, due to the presence of different patterns of glycosylation as well as multiple amino acid sequences at both N and C termini, were characterized on the purified molecule using complementary analytical techniques including electrophoresis, liquid chromatography and electrospray mass spectrometry. Four different N-terminal sequences were identified but simplified to a reproducible ratio of two sequences, the mature form and a form starting at Ala3, by adjustment of the process conditions. Molecules lacking 1-6 residues at the C-terminus were identified and their relative frequencies quantified. Amino acid modifications, such as three oxidized Met residues at positions 79, 141 and 187 and one deamidated Asn residue at position 176, were detected at low level. Microheterogeneities in glycosylation were characterized on four different sites, one located in the GM-CSF portion and three in the IL-3 portion of the molecule. The sites were shown to be differentially occupied and to carry 0-10 mannose residues according to their location in the sequence. Precise measurement of the heterogeneities at the molecular level were used to tune the process conditions and ensure reproducibility of the clinical product between lots.

Amino Acid Sequence↗
PubMed1996

Partitioning of a-factor analogues into membranes: analysis of binding and importance for biological activity.

Analogues of the a-factor mating pheromone of the yeast Saccharomyces cerevisiae were used to measure interactions of the pheromones with lipid vesicles and with isolated yeast membranes. The binding of the analogues of a-factor to vesicles and to membranes was best described as a partitioning of the pheromones into the lipid phase. The partitioning was enhanced by the negative surface potential of the membranes and was well described by the Gouy-Chapman theory of diffuse double layers. From the analysis of the binding of the pheromones to synthetic vesicles of known surface potential, effective charges and intrinsic partition coefficients were obtained for the pheromones. The information was used in subsequent experiments with yeast membranes to determine the intrinsic partition coefficients of the a-factor analogues and the charge density of the yeast membranes. Derivatives of a-factor with different alkyl chains in place of the normal C-terminal farnesyl displayed biological activity that paralleled the degree of partitioning of the pheromones into vesicles. Demethylation of the C-terminus decreased the partition coefficient by 6-fold and decreased the biological activity of the pheromone by greater than 2500-fold. The results show that a-factor can effectively partition into membrane bilayers and that the partitioning is probably involved in the subsequent recognition of the pheromone by the a-factor receptor.

4-Butyrolactone↗
PubMed1964

EFFECT OF DRUG-RESISTANCE FACTOR R ON THE F PROPERTIES OF ESCHERICHIA COLI.

Hirota, Yukinori (Osaka University, Osaka, Japan), Yukinobu Nishimura, Frits Ørskov, and Ida Ørskov. Effect of drug-resistance factor R on the F properties of Escherichia coli. J. Bacteriol. 87:341-351. 1964.-Infection of Escherichia coli male cells (Hfr or F(+)) with resistance factor R results in the co-ordinate inhibition of several distinct functions of F factor: mating capacity to transfer chromosome by conjugation, production of f(+) antigen, and formation of receptors for the male-specific bacteriophages, f1 and ribonucleic acid phage. The i(-) mutant (R(100-1)) of R factor, which was isolated from wild-type R factor (R(100)), shows no inhibition of these F properties. Male R(+) (100-1) cells were autoagglutinable but the f(+) antigen was still present. When R-infected female cells had acquired the ability to form recombinants with an F(-) strain, they also had become autoagglutinable. The question of the presence of f(+) antigen in these strains was not solved. The cause of the autoagglutinability is not known, but it is not the result of loss of O antigen (rough autoagglutinability). Sensitivity to a phage tau, which can form plaques on female cells only, is not affected by the presence or absence of R factor. No difference in the pattern of segregation of recombinants was observed between the cross of Hfr R(-) x F(-) and that of Hfr R(+) x F(-). These results indicate that R factor controls a key mechanism in the synthesis of "F substances" formed on the cell surface by the F factor.

Agglutination↗