Dielectric behavior of linear polyelectrolytes

The dipolar correlation function for a system of counterions diffusing on the surface of a polyelectrolyte cylinder is computed. Repulsive coulombic interactions between the counterions are taken into account. Lateral dissociation and reassociation to the cylinder is treated microscopically. Numerical calculations needed to obtain quantitative results for the long time behavior are presented. The model dependence on its parameters is interpreted with special emphasis on parameter values typical of DNA.     

Homologies between members of the germin gene family in hexaploid wheat and similarities between these wheat germins and certain Physarum spherulins

By screening approximately 10(6) plaques in a wheat DNA library with a "full-length" germin cDNA probe, two genomic clones were detected. When digested with EcoRI, one clone yielded a 2.8-kilobase pair fragment (gf-2.8) and the other yielded a 3.8-kilobase pair fragment (gf-3.8). By nucleotide sequencing, each of gf-2.8 and gf-3.8 was found to encode a complete sequence for germin and germin mRNA, and to contain appreciable amounts of 5'- and 3'-flanking sequences. The "cap" site in gf-2.8 was determined by primer extension and the corresponding site in gf-3.8 was deduced by analogy. The mRNA coding sequences in gf-2.8 and gf-3.8 are intronless and 87% homologous with one another. The 5'-flanking regions in gf-2.8 and gf-3.8 contain recognizable sites of what are probably cis-acting elements but there is otherwise little if any significant similarity between them. In addition to putative TATA and CAAT boxes in the 5'-flanking regions of gf-2.8 and gf-3.8, there are AT-rich inverted-repeats, GC boxes, long purine-rich sequences, two 19-base pair direct-repeat sequences in gf-2.8, and a remarkably long (200-base pair) inverted-repeat sequence (approximately 90% homology) in gf-3.8. An 8% difference between the mature-protein coding regions in gf-2.8 and gf-3.8 is reflected by a corresponding 7% difference between the corresponding 201-residue proteins. Most significantly, the same 8% difference between the mature-protein coding regions in gf-2.8 and gf-3.8 is allied with no change whatever in a central part (61-151) of the encoded polypeptide sequences. It seems likely that this central, strongly conserved core in the germins is of first importance in the biochemical involvements of the proteins. When an equivalence is assumed between like amino acids, the gf-2.8 and gf-3.8 germins show significant (approximately 44%) similarity to spherulins 1a and 1b of Physarum polycephalum, a similarity that increases to approximately 50% in the conserved core of germin. Near the middle (87-96) of the conserved core in the germins is a rare PH(I/T)HPRATEI decapeptide sequence which is shared by spherulins (1a and 1b) and germins (gf-2.8 and gf-3.8). These similarities are discussed in the context of evidence which can be interpreted to suggest that the biochemistry of germins and spherulins is involved with cellular, perhaps cell-wall responses to desiccation, hydration, and osmotic stress.(ABSTRACT TRUNCATED AT 400 WORDS)     

Regulation of Noradrenaline Release from Rat Occipital Cortex Tissue Chops by α2-Adrenergic Agonists

Noradrenaline (NA) and the alpha 2-adrenergic agonists clonidine, BHT-920, and UK 14304-18 inhibit potassium-evoked release of [3H]NA from rat occipital cortex tissue chops with similar potencies. NA (10(-5) M) was most effective as up to 85% inhibition could be observed compared with 75%, 55%, and 35% for UK 14304-18, clonidine, and BHT-920, respectively, all at 10(-5) M. Potassium-evoked release was enhanced by both forskolin (10(-5) M) and 1 mM dibutyryl cyclic AMP. Pretreatment of tissue chops with 1 mM dibutyryl cyclic AMP in the presence of 3-isobutyl-1-methylxanthine partially reversed the alpha 2-adrenergic agonist inhibition of NA release. No reversal of inhibition was observed following pretreatment with 10(-5) M forskolin. The effects of clonidine, BHT-920, UK-14308-18, and NA on cyclic AMP formation stimulated by (a) forskolin, (b) isoprenaline, (c) adenosine, (d) potassium, and (e) NA were examined. Only cAMP formation stimulated by NA was inhibited by these alpha 2-adrenergic agonists. These results suggest that only a small fraction of adenylate cyclase in rat occipital cortex is coupled to alpha 2-adrenergic receptors. These results are discussed in relation to recent findings that several alpha 2-adrenergic receptor subtypes occur, not all of which are coupled to the inhibition of adenylate cyclase, and that alpha 2-adrenergic receptors inhibit NA release in rat occipital cortex by a mechanism that does not involve decreasing cyclic AMP levels.     

Neuronal cell adhesion molecule contactin/F11 binds to tenascin via its immunoglobulin-like domains

Adhesive interactions between neurons and extracellular matrix (ECM) play a key role in neuronal pattern formation. The prominent role played by the extracellular matrix protein tenascin/cytotactin in the development of the nervous system, tied to its abundance, led us to speculate that brain may contain yet unidentified tenascin receptors. Here we show that the neuronal cell adhesion molecule contactin/F11, a member of the immunoglobulin(Ig)-superfamily, is a cell surface ligand for tenascin in the nervous system. Through affinity chromatography of membrane glycoproteins from chick brain on tenascin-Sepharose, we isolated a major cell surface ligand of 135 kD which we identified as contactin/F11 by NH2-terminal sequencing. The binding specificity between contactin/F11 and tenascin was demonstrated in solid-phase assays. Binding of immunopurified 125I-labeled contactin/F11 to immobilized tenascin is completely inhibited by the addition of soluble tenascin or contactin/F11, but not by fibronectin. When the fractionated isoforms of tenascin were used as substrates, contactin/F11 bound preferentially to the 190-kD isoform. This isoform differs in having no alternatively spliced fibronectin type III domains. Our results imply that the introduction of these additional domains in some way disrupts the contactin/F11 binding site on tenascin. To localize the binding site on contactin/F11, proteolytic fragments were generated and characterized by NH2-terminal sequencing. The smallest contactin/F11 fragment which binds tenascin is 45 kD and also begins with the contactin/F11 NH2-terminal sequence. This implies that contactin/F11 binds to tenascin through a site within the first three Ig-domains.     

The effect of 2,2'-dichlorodiethyl sulfide on DNA synthesis of a murine stratified keratinocyte culture system.

A primary stratified keratinocyte culture resembling the epidermis in situ was used as a model for studying the effects of exposure to 2,2'-dichlorodiethyl sulfide, or sulfur mustard (SM), on DNA synthesis. A method that distinguishes between semi-conservative (s.c.) DNA synthesis and repair synthesis was used to determine if the former was inhibited following treatment with SM. In this method the density of the newly synthesized DNA was increased by incorporation of 5-bromo-2-deoxyuridine. Density gradient centrifugation was then used to isolate the heavy DNA for quantification. It was demonstrated that topically applied SM in the dose range of 1-10 nmole/cm2 inhibited s.c. DNA synthesis (replication) in a dose and time related manner. Inhibition of DNA replication by SM would result in inhibition of cell division which must be preceded by s.c. DNA synthesis. This failure to replace damaged germinative cells may lead to the destruction of the basal layer which is observed in vivo and in our epidermal culture following exposure to SM. This may also be related to development of vesication observed in exposed intact human skin.     

Sulfate reduction and S-oxidation in a moorland pool sediment

In an oligotrophic moorland pool in The Netherlands, S cycling near the sediment/water boundary was investigated by measuring (1) SO₄ ^2– reduction rates in the sediment, (2) depletion of SO₄ ^2– in the overlying water column and (3) release of³⁵S from the sediment into the water column. Two locations differing in sediment type (highly organic and sandy) were compared, with respect to reduction rates and depletion of SO₄ ^2– in the overlying water.Sulfate reduction rates in sediments of an oligotrophic moorland pool were estimated by diagenetic modelling and whole core³⁵SO₄ ^2– injection. Rates of SO₄ ^2– consumption in the overlying water were estimated by changes in SO₄ ^2– concentration over time in in situ enclosures. Reduction rates ranged from 0.27–11.2 mmol m^–2 d^–1. Rates of SO₄ ^2– uptake from the enclosed water column varied from –0.5, –0.3 mmol m^–2 d^–1 (November) to 0.43–1.81 mmol m^–2 d^–1 (July, August and April). Maximum rates of oxidation to SO₄ ^2– in July 1990 estimated by combination of SO₄ ^2– reduction rates and rates of in situ SO₄ ^2– uptake in the enclosed water column were 10.3 and 10.5 mmol m^–2 d^–1 at an organic rich and at a sandy site respectively.Experiments with³⁵S^2– and³⁵SO₄ ^2– tracer suggested (1) a rapid formation of organically bound S from dissimilatory reduced SO₄ ^2– and (2) the presence of mainly non SO₄ ^2–-S derived from reduced S transported from the sediment into the overlying water. A³⁵S^2– tracer experiment showed that about 7% of³⁵S^2– injected at 1 cm depth in a sediment core was recovered in the overlying water column.Sulfate reduction rates in sediments with higher volumetric mass fraction of organic matter did not significantly differ from those in sediments with a lower mass fraction of organic matter.Corresponding author     

Multiple forms of Go alpha mRNA: analysis of the 3'-untranslated regions

Go, a guanine nucleotide binding protein found predominantly in neural tissues, interacts in vitro with rhodopsin, muscarinic, and other receptors and has been implicated in the regulation of ion channels. Despite the virtual identity of reported cDNA sequences for the alpha subunit of Go (Go alpha), multiple molecular weight forms of mRNA have been identified in tissues from all species examined. To investigate the molecular basis for the size heterogeneity of Go alpha mRNAs, four cDNA clones were isolated from the same retinal lambda gt10 cDNA library that was used earlier to isolate lambda GO9, a clone encompassing the complete coding region of Go alpha. These clones were identified as Go alpha clones based on nucleotide sequence identity with lambda GO9 in the coding region; they diverge, however, from lambda GO9 in the 3'-untranslated region 28 nucleotides past the stop codon. An oligonucleotide probe complementary to a portion of the 3'-untranslated region of lambda GO9 that differs from the newly isolated clones hybridized with 3.0- and 4.0-kb mRNAs present in bovine brain and retina whereas a similar probe for the unique region of the new clones hybridized with a 4.0-kb mRNA in both tissues and with a 2.0-kb mRNA found predominantly in retina. A similar hybridization pattern was observed when brain poly(A+) RNA from other species was hybridized with the different 3'-untranslated region probes. It appears that differences in the 3'-untranslated regions could, in part, be the basis for the observed heterogeneity in Go alpha mRNAs.     

The vacuum UV CD bands of repeating DNA sequences are dependent on sequence and conformation

CD spectra were obtained for eight synthetic double-stranded DNA polymers down to at least 175 nm in the vacuum uv. Three sets of sequence isomers were studied: (a) poly[d(A-C).d(G-T)] and poly[d(A-G).d(C-T)], (b) poly[d(A-C-C).d(G-G-T)] and poly[d(A-C-G).d(C-G-T)], and (c) poly[d(A).d(T)], poly[d(A-T).d(A-T)], poly[d(A-A-T).d(A-T-T)], and poly[d(A-A-T-T).d(A-A-T-T)]. There were significant differences in the CD spectra at short wavelengths among each set of sequence isomers. The (G.C)-containing sequences had the largest vacuum uv bands, which were positive and in the wavelength range of 180-191 nm. There were no large negative bands at longer wavelengths, consistent with the polymers all being in right-handed conformations. Among the set of sequences containing only A.T base pairs, poly[d(A).d(T)] had the largest vacuum uv CD band, which was at 190 nm. This CD band was not present in the spectra of the other (A.T)-rich polymers and was absent from two first-neighbor estimations of the poly[d(A).d(T)] spectrum obtained from the other three sequences. We concluded that the sequence dependence of the vacuum uv spectra of the (A.T)-rich polymers was due in part to the fact that poly[d(A).d(T)] exists in a noncanonical B conformation.