A small family of novel basic leucine zipper proteins that includes abscisic acid (ABA)-INSENSITIVE 5 (ABI5) binds to the promoter region of the lea class gene Dc3. The factors, referred to as AtDPBFs (Arabidopsis Dc3 promoter-binding factors), were isolated from an immature seed cDNA library. AtDPBFs bind to the embryo specification and ABA-responsive elements in the Dc3 promoter and are unique in that they can interact with cis-elements that do not contain the ACGT core sequence required for the binding of most other plant basic leucine zipper proteins. Analysis of full-length cDNAs showed that at least five different Dc3 promoter-binding factors are present in Arabidopsis seeds; one of these, AtDPBF-1, is identical to ABI5. As expected, AtDPBF-1/ABI5 mRNA is inducible by exogenous ABA in seedlings. Despite the near identity in their basic domains, AtDPBFs are distinct in their DNA-binding, dimerization, and transcriptional activity.LEA (late embryogenesis abundant) genes as a group are highly expressed during late stages of embryo development (Hughes and Galau, 1991;Thomas, 1993;Parcy et al., 1994). lea gene products are ubiquitous among higher plants, and they are probably involved in the protection of cells from dehydration (Dure et al., 1989; Dure, 1993; Ingram and Bartels, 1996;Xu et al., 1996). Expression of many lea genes is not only seed specific but is also inducible by abscisic acid (ABA) or environmental stresses such as drought and high salinity (Skriver and Mundy, 1990; Chandler and Robertson, 1994; Ingram and Bartels, 1996).Dc3 is a carrot (Daucus carota) lea class gene that is abundantly expressed during somatic embryogenesis (Wilde et al., 1988). The Dc3 promoter drives ␤-glucuronidase (GUS) reporter gene expression in developing seeds of transgenic tobacco (Nicotiana tabacum) and in nonembryonic tissues exposed to exogenous ABA and conditions of water deficit (Seffens et al., 1990;Vivekananda et al., 1992;Siddiqui et al., 1998). Analysis of the Dc3 promoter revealed minimal sequences necessary for embryo-specific expression residing within a 117-bp region including the transcription start site (Thomas, 1993; Chung, 1996;Thomas et al., 1997). However, this proximal promoter region (PPR) is not sufficient for ABAinduced expression; the distal promoter region (DPR), located between Ϫ314 and Ϫ287, is also required for ABA response in addition to the PPR (Chung, 1996;Thomas et al., 1997). The PPR contains five related cis regulatory elements required for expression in embryogenesis; these elements (E motifs) share the consensus sequence ACACNNG. Elements with NNNCGTGT consensus are repeated within the minimal DPR. These latter elements are similar to the E motifs. The function of these elements has been demonstrated in planta (Chung, 1996).Protein-binding studies showed that similar, seedspecific, or ABA-inducible protein factors bind to the PPR and the DPR. Competition DNA-binding assays indicated that similar factors can bind to both the PPR and the DPR. Genes encoding these Dc3 promoterbindin...

Selected channel-lining cysteine mutants from the M2 segment of rat ␣1 ␥-aminobutyric acid (GABA) type A receptor subunit, at positions 257, 261, 264, and 272 were co-expressed with ␤1 and ␥2 subunits in Xenopus oocytes. They generated functional receptors displaying conductance and response to both GABA and picrotoxinin similar to the wild type ␣1␤1␥2 receptor. Three chemically reactive affinity probes derived from noncompetitive blockers were synthesized to react with the engineered cysteines: 1) dithiane bis-sulfone derivative modified by an isothiocyanate function (probe A); 2) fiprole derivatives modified by an ␣-chloroketone (probe B) and ␣-bromoketone (probe C) moiety. These probes blocked the GABA-induced currents on all receptors. This blockade could be fully reversed by a washing procedure on the wild type, the ␣1T261C␤1␥2 and ␣1L264C␤1␥2 mutant receptors. In contrast, an irreversible effect was observed for all three probes on both ␣1V257C␤1␥2 and ␣1S272C␤1␥2 mutant receptors. This effect was probe concentration-dependent and could be abolished by picrotoxinin and/or t-butyl bicyclophosphorothionate. These data indicate a major interaction of non-competitive blockers at position 257 of the presumed M2 segment of rat ␣1 subunit but also suggest an interaction at the more extracellular position 272. ␥-Aminobutyric acid type A (GABA A ) 1 receptors exert their inhibitory effect in the central nervous system of vertebrates by regulating a chloride-sensitive channel which is very likely centered within a protein transmembrane heteropentameric subunits complex (1-5). The existence of 6␣, 4␤, 4␥, 1␦, and 2 subunits in addition to splicing variants, suggests a large diversity in the constitution of heteropentameric isoforms allowing a subtle tuning of the action of this neurotransmitter (6 -8). However, it has been proposed that a restricted number of combinations condition the functioning of this receptor and it is assumed that the ␣1␤2␥2 represents the major adult isoform (9). GABA A receptors serve as the target for several classes of molecules including important neuroactive drugs such as benzodiazepines, barbiturates, and neurosteroids. In contrast, only three receptor subunits have been cloned from insects up to now, RDL (10), ␤ (11), and GRD (12) leading to an apparently less complex situation for their structural assembly. Of particular interest are the action of non-competitive antagonists which are presumed to interact within the GABA receptor chloride channel leading to powerful insecticidal properties when presenting a selectivity for insect GABA receptor (13-16).To investigate, at a molecular level, the interaction of noncompetitive GABA antagonists with the chloride channel associated to the GABA A receptor, we defined an approach which uses chemically reactive non-competitive blockers (NCBs) as chemical sensors for cysteine mutants on the rat ␣1 GABA receptor subunit. This strategy was derived from the extensive work of Akabas and co-workers on several ionic channels including the chloride chan...

No abstract

No abstract

Lead dioxide thin films and nanowires were prepared by electrochemical deposition using a 0.1M Pb(NnormalO3)2 solution. α-PbnormalO2 is deposited at pH 5.0, while β-PbnormalO2 is obtained at pH 0.0. Using pH 5.0, films of different thicknesses and nanowires of different lengths were prepared by varying the deposition charge (Qdep) . The electrochemical reactivity of PbnormalO2 is strongly dependent on the structure of the deposit. For PbnormalO2 nanowires and thin films, only ∼6to7% and 2–3% of the deposited material is electrochemically active, respectively. A detailed analysis of the reactivity of PbnormalO2 with the deposition of PbnormalO2 with the deposition charge was performed by assuming that r=aQdepb , where r is the percentage of reactive matter, and a and b are adjustable parameters. For PbnormalO2 nanowires, b=−0.2 and the reactivity is almost independent of the deposition charge (and length of the nanowires). In contrast, for PbnormalO2 thin films, b=−0.65 and the reactivity decreases rapidly with the reciprocal of the deposition charge. After 10cycles , PbnormalO2 nanowires and thin films exhibit almost the same activity.