University of Groningen

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    68908 research outputs found

    Self-Employment of Immigrants: A Cross-National Study of 17 Western Societies

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    This study examines the role of immigrants’ country of origin, country of destination and combinations thereof (settings or communities) in the likelihood of immigrants being selfemployed. I pooled census data from three classic immigrant countries (Australia, Canada and the United States) and labor-force surveys from 14 countries in the European Union for a cross-national data set. Using multilevel techniques, I find that (1) immigrants from non-Christian countries of origin have higher odds of self-employment, (2) higher levels of unemployment among natives increase the odds of self-employment, and (3) selfemployment is more frequent among immigrant communities that are small, highly educated and have a longer settlement history.

    The Lantibiotic Nisin Induces Transmembrane Movement of a Fluorescent Phospholipid

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    Nisin is a pore-forming antimicrobial peptide. The capacity of nisin to induce transmembrane movement of a fluorescent phospholipid in lipid vesicles was investigated. Unilamellar phospholipid vesicles that contained a fluorescent phospholipid (1-acyl-2-{6-[(7-nitro-2-1,3-benzoxadiazol-4-yl)amino]caproyl}-sn-glycero-3-phosphocholine) in the inner leaflet of the bilayer were used. Nisin-induced movement of the fluorescent phospholipid from the inner leaflet to the outer leaflet of the membrane reached stable levels, which were dependent on the concentration of nisin added. The rate constant k of this nisin-induced transmembrane movement increased with the nisin concentration but was not dependent on temperature within the range of 5 to 30°C. In contrast, the rate constant of movement of fluorescent phospholipid from vesicle to vesicle strongly depended on temperature. The data indicate that nisin transiently disturbs the phospholipid organization of the target membrane.

    Expression systems for industrial Gram-positive bacteria with low guanine and cytosine content

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    Recent years have seen an increase in the development of gene expression systems for industrial Gram-positive bacteria with low guanine and cytosine content that belong to the genera Bacillus, Clostridium, Lactococcus, Lactobacillus, Staphylococcus and Streptococcus. In particular, considerable advances have been made in the construction of inducible gene expression systems based on the capacity of these bacteria to utilize specific sugars or to secrete autoinducing peptides that are involved in quorum sensing. These controlled expression systems allow for present and future exploitation of these bacteria as cell factories in medical, agricultural, and food biotechnology.

    From DNA sequence to application: possibilities and complications

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    The development of sophisticated genetic tools during the past 15 years have facilitated a tremendous increase of fundamental and application-oriented knowledge of lactic acid bacteria (LAB) and their bacteriophages. This knowledge relates both to the assignments of open reading frames (ORF’s) and the function of non-coding DNA sequences. Comparison of the complete nucleotide sequences of several LAB bacteriophages has revealed that their chromosomes have a fixed, modular structure, each module having a set of genes involved in a specific phase of the bacteriophage life cycle. LAB bacteriophage genes and DNA sequences have been used for the construction of temperature-inducible gene expression systems, gene-integration systems, and bacteriophage defence systems. The function of several LAB open reading frames and transcriptional units have been identified and characterized in detail. Many of these could find practical applications, such as induced lysis of LAB to enhance cheese ripening and re-routing of carbon fluxes for the production of a specific amino acid enantiomer. More knowledge has also become available concerning the function and structure of non-coding DNA positioned at or in the vicinity of promoters. In several cases the mRNA produced from this DNA contains a transcriptional terminator-antiterminator pair, in which the antiterminator can be stabilized either by uncharged tRNA or by interaction with a regulatory protein, thus preventing formation of the terminator so that mRNA elongation can proceed. Evidence has accumulated showing that also in LAB carbon catabolite repression in LAB is mediated by specific DNA elements in the vicinity of promoters governing the transcription of catabolic operons. Although some biological barriers have yet to be solved, the vast body of scientific information presently available allows the construction of tailor-made genetically modified LAB. Today, it appears that societal constraints rather than biological hurdles impede the use of genetically modified LAB.

    The Hansenula polymorpha PER8 Gene Encodes a Novel Peroxisomal Integral Membrane Protein Involved in Proliferation

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    We previously described the isolation of mutants of the methylotrophic yeast Hansenula polymorpha that are defective in peroxisome biogenesis. Here, we describe the characterization of one of these mutants, per8, and the cloning of the PER8 gene. In either methanol or methylamine medium, conditions that normally induce the organdies, per8 cells contain no peroxisome-like structures and peroxisomal enzymes are located in the cytosol. The sequence of PER8 predicts that its product (Per8p) is a novel polypeptide of 34 kD, and antibodies against Per8p recognize a protein of 31 kD. Analysis of the primary sequence of Per8p revealed a 39-amino-acid cysteine-rich segment with similarity to the C3HC4 family of zinc-finger motifs. Overexpression of PER8 results in a markedly enhanced increase in peroxisome numbers. We show that Per8p is an integral membrane protein of the peroxisome and that it is concentrated in the membranes of newly formed organdies. We propose that Per8p is a component of the molecular machinery that controls the proliferation of this organelle.

    Geometrical Aspects of Stability Theory for Hill's Equations

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    Type II duality symmetries in six dimensions

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    We discuss the different discrete duality symmetries in six dimensions that act within and between (i) the 10-dimensional heterotic string compactified on T^4, (ii) the 10-dimensional type IIA string compactified on K3 and (iii) the 10-dimensional type IIB string compactified on K3. In particular we show that the underlying group-theoretical structure of these discrete duality symmetries is determined by the proper cubic group C/Z2. Our group theoretical interpretation leads to simple rules for constructing the explicit form of the different discrete type II duality symmetries in an arbitrary background. The explicit duality rules we obtain are applied to construct dual versions of the 6-dimensional chiral null model.

    Partner’s and own education: does who you live with matter for self-assessed health, smoking and excessive alcohol consumption?

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    This study analyses the importance of partner status and partner’s education, adjusted for own education, on selfassessed health, smoking and excessive alcohol consumption. The relationship between socio-economic factors and health-related outcomes is traditionally studied from an individual perspective. Recently, applying social–ecological models that include socio-economic factors on various social levels is becoming popular. We argue that partners are an important influence on individual health and health-related behaviour at the household level. Therefore, we include partners in the analysis of educational health inequalities. Using data of almost 40,000 individuals (with almost 15,000 Dutch cohabiting couples), aged 25–74 years, who participated in the Netherlands Health Interview Survey between 1989 and 1996, we test hypotheses on the importance of own and partner’s education. We apply advanced logistic regression models that are especially suitable for studying the relative influence of partners’ education. Controlled for own education, partner’s education is significantly associated with self-assessed health and smoking, for men and women. Accounting for both partners’ education the social gradient in self-assessed health and smoking is steeper than based on own or partner’s education alone. The social gradient in health is underestimated by not considering partner’s education, especially for women.

    Reinforced molecular recognition as an alternative to rigid receptors

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    In theory, a perfectly rigid receptor will probably be an unbeatable binder. However, rigidity may not be easy to achieve in practice and it is certainly not Nature’s method to realise high affinity. In many proteins binding affinity is increased through non-covalent interactions within the protein. Thus there is a considerable incentive to follow Nature’s example and start exploring the use of secondary intra-receptor interactions to aid in the binding process. Secondary interactions within a receptor will reinforce host–guest binding when the same conformational rearrangement (or freezing of motion) is required for guest binding as for the formation of the intra-receptor interactions. Introducing secondary interactions will require rather elaborate synthetic receptors to be produced. With the recent developments in dynamic combinatorial chemistry, access to the desired structures should be facilitated. Whether or not this approach will develop into a practical method remains to be established, but even if it does not, efforts along these lines will lead to a better understanding of the complex interplay between molecular recognition, folding and dynamics.


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