1,569 research outputs found

    Intrinsic Gating Properties of a Cloned G Protein-activated Inward Rectifier K^+ Channel

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    The voltage-, time-, and K^+-dependent properties of a G protein-activated inwardly rectifying K^+ channel (GIRK1/KGA/Kir3.1) cloned from rat atrium were studied in Xenopus oocytes under two-electrode voltage clamp. During maintained G protein activation and in the presence of high external K^+ (V_K = 0 mV), voltage jumps from V_K to negative membrane potentials activated inward GIRK1 K^+ currents with three distinct time-resolved current components. GIRK1 current activation consisted of an instantaneous component that was followed by two components with time constants T_f~50 ms and T_s~400 ms. These activation time constants were weakly voltage dependent, increasing approximately twofold with maximal hyperpolarization from V_K. Voltage-dependent GIRK1 availability, revealed by tail currents at -80 mV after long prepulses, was greatest at potentials negative to V_K and declined to a plateau of approximately half the maximal level at positive voltages. Voltage-dependent GIRK1 availability shifted with V_K and was half maximal at V_K -20 mV; the equivalent gating charge was ~1.6 e^-. The voltage-dependent gating parameters of GIRK1 did not significantly differ for G protein activation by three heterologously expressed signaling pathways: m2 muscarinic receptors, serotonin 1A receptors, or G protein β1y2 subunits. Voltage dependence was also unaffected by agonist concentration. These results indicate that the voltage-dependent gating properties of GIRK1 are not due to extrinsic factors such as agonist-receptor interactions and G protein-channel coupling, but instead are analogous to the intrinsic gating behaviors of other inwardly rectifying K^+ channels

    Fast, easy and efficient: site-specific insertion of transgenes into Enterobacterial chromosomes using Tn7 without need for selection of the insertion event

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    BACKGROUND: Inserting transgenes into bacterial chromosomes is generally quite involved, requiring a selection for cells carrying the insertion, usually for drug-resistance, or multiple cumbersome manipulations, or both. Several approaches use phage λ red recombination, which allows for the possibility of mutagenesis of the transgene during a PCR step. RESULTS: We present a simple, rapid and highly efficient method for transgene insertion into the chromosome of Escherichia coli, Salmonella or Shigella at a benign chromosomal site using the site-specific recombination machinery of the transposon Tn7. This method requires very few manipulations. The transgene is cloned into a temperature-sensitive delivery plasmid and transformed into bacterial cells. Growth at the permissive temperature with induction of the recombination machinery leads to transgene insertion, and subsequent growth at the nonpermissive temperature cures the delivery plasmid. Transgene insertion is highly site-specific, generating insertions solely at the Tn7 attachment site and so efficient that it is not necessary to select for the insertion. CONCLUSION: This method is more efficient and straightforward than other techniques for transgene insertion available for E. coli and related bacteria, making moving transgenes from plasmids to a chromosomal location a simple matter. The non-requirement for selection is particularly well suited for use in development of unmarked strains for environmental release, such as live-vector vaccine strains, and also for promoter-fusion studies, and experiments in which every bacterial cell must express a transgene construct

    Site-specific Tn7 transposition into the human genome

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    The bacterial transposon, Tn7, inserts into a single site in the Escherichia coli chromosome termed attTn7 via the sequence-specific DNA binding of the target selector protein, TnsD. The target DNA sequence required for Tn7 transposition is located within the C-terminus of the glucosamine synthetase (glmS) gene, which is an essential, highly conserved gene found ubiquitously from bacteria to humans. Here, we show that Tn7 can transpose in vitro adjacent to two potential targets in the human genome: the gfpt-1 and gfpt-2 sequences, the human analogs of glmS. The frequency of transposition adjacent to the human gfpt-1 target is comparable with the E.coli glmS target; the human gfpt-2 target shows reduced transposition. The binding of TnsD to these sequences mirrors the transposition activity. In contrast to the human gfpt sequences, Tn7 does not transpose adjacent to the gfa-1 sequence, the glmS analog in Saccharomyces cerevisiae. We also report that a nucleosome core particle assembled on the human gfpt-1 sequence reduces Tn7 transposition by likely impairing the accessibility of target DNA to the Tns proteins. We discuss the implications of these findings for the potential use of Tn7 as a site-specific DNA delivery agent for gene therapy

    Adapting a Curriculum Unit to Facilitate Interaction Between Technology, Mathematics and Science in the Elementary Classroom: Identifying Relevant Criteria

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    Calls for the integration of subjects continue to emanate from a wide range of professional bodies, including governments and subject associations. Yet as some authors suggest, blurring the boundaries between subjects may be one of the most daunting tasks educators face. The authors have recently begun a research study that will investigate the extent to which (a) relevant mathematics and science can be made explicit in a technology curriculum unit, (b) pupils utilise this mathematics and science learning, and (c) pupils' ability to design is enhanced by making the mathematics and science explicit and useful. This paper reports the results of Phase 1 of the study: an examination of research literature in order to identify criteria to inform the re-writing of an existing technology curriculum (to be used as a research instrument) that previously did not make explicit embedded mathematics and science concepts. Our reading of the literature has identified two essential criteria that must be met during the re-writing: (a) protecting the integrity of the subjects and (b) identifying the nature and purpose of the intended learning
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