122 research outputs found

    Representing homology classes of simply connected 4-manifolds

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    AbstractThe main theorem asserts that every 2-dimensional homology class of a compact simply connected PL 4-manifold can be represented by a codimension-0 submanifold consisting of a contractible manifold with a single 2-handle attached. One consequence of the theorem is the fact that every map of S2 into a simply connected, compact PL 4-manifold is homotopic to an embedding if and only if the same is true for every homotopy equivalence. The theorem is also the main ingredient in the proof of the following result: If W is a compact, simply connected, PL submanifold of S4, then each element of H2(W;Z) can be represented by a locally flat topological embedding of S2

    Salt-inducible promoter derivable from a lactic acid bacterium, and its use in a lactic acid bacterium for production of a desired protein

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    The invention provides a salt-inducible promoter present in SEQ ID NO: 10 and derivable from a lactic acid bacterium in isolation from the coding sequence normally controlled by said promoter in a wild-type lactic acid bacterium, with modifications and important parts thereof. Also provided are a recombinant vector and a transformed lactic acid bacterium comprising such promoter, and the production of a desired protein by such transformed bacterium, whereby the gene encoding said desired protein or a precursor thereof is expressed under control of such promoter. The desired protein can be secreted by the bacterium due to the presence of a signal sequence. The action of the salt-inducible promoter is enhanced at a pH of about 4-4.5 and/or by the presence of glutamic acid. Such process can be used in a fermentation process, in which the desired protein is a lytic protein causing lysis of the cells and release of the cell content. Or the desired protein can be an enzyme involved in flavour formation, e.g. in producing dressings, spreads, sausages and sour dough, or a protein functioning in a cheese production process, such as chymosin or a precursor thereof, or an enzyme involved in cheese flavour formation

    Mechanism of Transcription Activation at the comG Promoter by the Competence Transcription Factor ComK of Bacillus subtilis

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    The development of genetic competence in Bacillus subtilis is regulated by a complex signal transduction cascade, which results in the synthesis of the competence transcription factor, encoded by comK. ComK is required for the transcription of the late competence genes that encode the DNA binding and uptake machinery and of genes required for homologous recombination. In vivo and in vitro experiments have shown that ComK is responsible for transcription activation at the comG promoter. In this study, we investigated the mechanism of this transcription activation. The intrinsic binding characteristics of RNA polymerase with and without ComK at the comG promoter were determined, demonstrating that ComK stabilizes the binding of RNA polymerase to the comG promoter. This stabilization probably occurs through interactions with the upstream DNA, since a deletion of the upstream DNA resulted in an almost complete abolishment of stabilization of RNA polymerase binding. Furthermore, a strong requirement for the presence of an extra AT box in addition to the common ComK-binding site was shown. In vitro transcription with B. subtilis RNA polymerase reconstituted with wild-type -subunits and with C-terminal deletion mutants of the -subunits was performed, demonstrating that these deletions do not abolish transcription activation by ComK. This indicates that ComK is not a type I activator. We also show that ComK is not required for open complex formation. A possible mechanism for transcription activation is proposed, implying that the major stimulatory effect of ComK is on binding of RNA polymerase.Peer reviewe

    Multiple-Peptidase Mutants of Lactococcus lactis Are Severely Impaired in Their Ability To Grow in Milk

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    To examine the contribution of peptidases to the growth of Lactococcus lactis in milk, 16 single- and multiple-deletion mutants were constructed. In successive rounds of chromosomal gene replacement mutagenesis, up to all five of the following peptidase genes were inactivated (fivefold mutant): pepX, pepO, pepT, pepC, and pepN. Multiple mutations led to slower growth rates in milk, the general trend being that growth rates decreased when more peptidases were inactivated. The fivefold mutant grew more than 10 times more slowly in milk than the wild-type strain. In one of the fourfold mutants and in the fivefold mutant, the intracellular pools of amino acids were lower than those of the wild type, whereas peptides had accumulated inside the cell. No significant differences in the activities of the cell envelope-associated proteinase and of the oligopeptide transport system were observed. Also, the expression of the peptidases still present in the various mutants was not detectably affected. Thus, the lower growth rates can directly be attributed to the inability of the mutants to degrade casein-derived peptides. These results supply the first direct evidence for the functioning of lactococcal peptidases in the degradation of milk proteins. Furthermore, the study provides critical information about the relative importance of the peptidases for growth in milk, the order of events in the proteolytic pathway, and the regulation of its individual components.