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This article examines the process of creating a collaborative art exhibition, 'Dis Nag2 - The Cape's Hidden Roots in Slavery' (23 September-10 October 1998) which took place at the Slave Lodge (then Cultural History Museum) in Cape Town, South Africa (now the site of a permanent exhibition on slavery, 'Remembering Slavery'3 ), as a means through which seemingly separate and particularised histories may be shared and collectively owned across cultural groups, in moving towards a collective national identity for South Africans. The role of the exhibition space is examined as a means of shaping, through praxis, new histories in the present; as well as considering the major tensions and contradictions involved within such transformative processes, with a consideration of how such processes relate to current debates in museology. The study is derived in part from previous research examining materiality, shifts in perceptions of self-identities away from racialised constructs in the new South Africa, and focusing on artmaking as a medium for social agency, performance and shifting self-identities for historically disadvantaged artists in Cape Town, South Africa. [ABSTRACT FROM AUTHOR]

During development of the primary olfactory projection, olfactory receptor axons must sort by odor specificity and seek particular sites in the brain in which to create odor-specific glomeruli. In the moth Manduca sexta, we showed previously that fasciclin II, a cell adhesion molecule in the immunoglobulin superfamily, is expressed by the axons of a subset of olfactory receptor neurons during development and that, in a specialized glia-rich “sorting zone,” these axons segregate from nonfasciclin II-expressing axons before entering the neuropil of the glomerular layer. The segregation into fasciclin II-positive fascicles is dependent on the presence of the glial cells in the sorting zone. Here, we explore the expression patterns for different isoforms of Manduca fasciclin II in the developing olfactory system. We find that olfactory receptor axons express transmembrane fasciclin II during the period of axonal ingrowth and glomerulus development. Fascicles of TM-fasciclin II+ axons target certain glomeruli and avoid others, such as the sexually dimorphic glomeruli. These results suggest that TM-fasciclin II may play a role in the sorting and guidance of the axons. GPI-linked forms of fasciclin II are expressed weakly by glial cells associated with the receptor axons before they reach the sorting zone, but not by sorting-zone glia. GPI-fasciclin II may, therefore, be involved in axon–glia interactions related to stabilization of axons in the nerve, but probably not related to sorting. [Copyright &y& Elsevier]

This article presents abstracts of several papers about economics published in the September 1964 issue of the journal the Manchester School. The paper Special Deposits As an Instrument of Monetary Policy, N. J. Gibson assessed the effectiveness of special deposits as an instrument of monetary policy and how they fit into the context of post-war monetary policy in Great Britain. While in the article A Reconsideration of Investment and Pricing Criteria in the Nationalised Industries, A. J. Merrett examined alternative investment and pricing policies for nationalized industries in the light of the proposition that since the costs of welfare maximization may be considerable and these costs enter into the function to be maximized.

Nitric oxide synthase recently has been shown to be present in olfactory receptor cells throughout development of the adult antennal (olfactory) lobe of the brain of the moth Manduca sexta. Here, we investigate the possible involvement of nitric oxide (NO) in antennal-lobe morphogenesis. Inhibition of NO signaling with a NO synthase inhibitor or a NO scavenger early in development results in abnormal antennal lobes in which neuropil-associated glia fail to migrate. A more subtle effect is seen in the arborization of dendrites of a serotonin-immunoreactive neuron, which grow beyond their normal range. The effects of NO signaling in these types of cells do not appear to be mediated by activation of soluble guanylyl cyclase to produce cGMP, as these cells do not exhibit cGMP immunoreactivity following NO stimulation and are not affected by infusion of a soluble guanylyl cyclase inhibitor. Treatment with Novobiocin, which blocks ADP-ribosylation of proteins, results in a phenotype similar to those seen with blockade of NO signaling. Thus, axons of olfactory receptor cells appear to trigger glial cell migration and limit arborization of serotonin-immunoreactive neurons via NO signaling. The NO effect may be mediated in part by ADP-ribosylation of target cell proteins.

The gaseous messenger nitric oxide (NO), with its ability to mediate both intercellular and intracellular communication, can play important roles in mediating cellular communication in both the development and the function of the nervous system. The authors investigated the possible role of NO signaling in the developing olfactory system (antennal lobe) of the moth Manduca sexta. NO synthase (NOS), the enzyme that generates NO, was localized by using immunocytochemistry, in situ hybridization, and nicotinamide adenine dinucleotide phosphate-diaphorase (NADPH-d) histochemistry. Although NADPH-d staining appears to be a poor indicator of the presence of NOS in this system, immunocytochemistry and in situ hybridization reveal that NOS is expressed in the axons of olfactory receptor neurons throughout development and in the perineurial sheath that covers the brain early in development. NOS is present in axon terminals as they form protoglomeruli, raising the possibility that NO mediates cell-cell interactions during antennal lobe development. NO-sensitive soluble guanylyl cyclase (sGC), one of the best characterized targets of NO, was localized in the developing olfactory system by using in situ hybridization and immunocytochemistry for the Manduca sexta sGCalpha1 subunit. The ability of the developing olfactory system to respond to exogenous NO also was examined by using cyclic guanosine monophosphate immunocytochemistry. sGC is expressed in mechanosensory neurons in the developing antenna and in many antennal lobe neurons in both the medial and lateral cell body clusters. Thus, NOS and sGC are expressed in a pattern that suggests that this signaling pathway may mediate intercellular communication during development of the olfactory system in Manduca sexta., (Copyright 2000 Wiley-Liss, Inc.)

The nitric oxide (NO)-cGMP signaling system is thought to play important roles in the function of the olfactory system in both vertebrates and invertebrates. One way of studying the role of NO in the nervous system is to study the distribution and properties of NO synthase (NOS), as well as the soluble guanylyl cyclases (sGCs), which are the best characterized targets of NO. We study NOS and sGC in the relatively simple and well characterized insect olfactory system of the hawkmoth, Manduca sexta. We have cloned Manduca sexta nitric oxide synthase (MsNOS) and two sGCs (MsGCalpha1 and MsGCbeta1), characterized their basic biochemical properties, and studied their expression in the olfactory system. The sequences of the Manduca genes are highly similar to their mammalian homologs and show similar biochemical properties when expressed in COS-7 cells. In particular, we find that MsGC functions as an obligate heterodimer that is stimulated significantly by NO. We also find that MsNOS has a Ca2+-sensitive NO-producing activity similar to that of mammalian neuronal NOS. Northern and in situ hybridization analyses show that MsNOS and the MsGCs are expressed in a complementary pattern, with MsNOS expressed at high levels in the antennae and the MsGCs expressed at high levels in a subset of antennal lobe neurons. The expression patterns of these genes suggest that the NO-sGC signaling system may play a role in mediating communication between olfactory receptor neurons and projection neurons in the glomeruli of the antennal lobe.

We describe a rapid colorimetric method for the detection of PCR products. Color generation is complete within 5 min of mixing reagents with a PCR. The method is simple and does not require affinity capture steps or special labeling to be carried out. The color development can be monitored by eye or a simple spectrophotometer can be used to read sample absorbance. We demonstrate the method by its use in the amplification refractory mutation system (ARMS) analysis [C. R. Newton, A. Graham, L. E. Heptinstall, S. J. Powell, C. Summers, N. Kalsheker, et al. (1989) Nucleic Acids Res. 17, 2503-2515] of cystic fibrosis [J. R. Riordan, J. M. Rommens, B. Kerem, N. Alon, R. Rozmahel, Z. Grzelczak, et al. (1989) Science 245, 1066-1073] and factor V [R. M. Bertina, B. P. C. Koeleman, T. Koster, F. R. Rosendaal, R. J. Dirven, H. de Ronde, P. A. van der Velden, and P. H. Reitsma (1994) Nature 369, 64-67] allelic variants., (Copyright 1997 Academic Press.)

We combined the amplification refractory mutation system (ARMS) and fluorescence polarization (FP) to give a homogeneous genomic DNA genotype analysis method. Oligonucleotide probes labeled with the fluorescein dyes fluorescein isothiocyanate and 5-([4,6-dichlorotriazin-2-yl]amino)fluorescein and the rhodamine dye 6-carboxyrhodamine were included in amplification mixes and were annealed to PCR products after amplification. Hybridization was accompanied by an increase in the FP of the probe. We demonstrated homogeneous genotyping by analyzing human DNA samples for delta F508 mutation status of the cystic fibrosis transmembrane conductance regulator gene. The genotypes determined with the method described herein were in full agreement with those obtained by the conventional application of ARMS. We also demonstrated the simultaneous detection of two PCR products in a single reaction. The assay method described is homogeneous and so obviates the necessity to open reaction vessels after amplification. This therefore eliminates PCR carryover contamination.

Adenine, thymine and cytosine PNA monomers have been prepared using 3-amino-1,2-propanediol as a starting material. The benzoyl group was used to protect the exocyclic amines of the heterocyclic bases of A and C PNA monomers and the backbone primary amine was protected with the monomethoxytrityl group. The thymine and cytosine PNA monomers were used in conjunction with standard DNA synthesis monomers to produce chimeric PNA DNA (PDC) oligomers. Ultraviolet melting studies confirmed that these oligomers form stable hybrids with complementary DNA strands and that mismatches in the DNA but more so in the PNA sections lead to duplex destabilisation.

The anti-HIV drug 4'-azidothymidine (ADRT) has been incorporated into DNA by the phosphoramidite method. The presence of the modified nucleotide was shown to have a minimal effect on duplex conformation and stability by CD spectroscopy and UV melting.

The crystal structure of the oligonucleotide d(CGCAAATTO8GGCG), containing the chemically modified base 8-hydroxydeoxyguanine (O8G), has been determined at 2.5-A resolution and refined to a crystallographic R-factor of 16.8%. The B-type DNA helix contains standard Watson-Crick base pairs except at the mismatch sites, where O8G adopts a syn conformation and forms hydrogen bonds to adenine in the anti conformation. The thermodynamic stability of the duplex was found by UV melting techniques to be intermediate between the native oligonucleotide d(CGCAAATTTGCG) and an oligonucleotide containing A.G mispairs d(CGCAAATTGGCG). Comparison of the structure of the O8G(syn).A(anti) base pair with those of Watson-Crick base pairs has given a reason why O8G.A base pairs are not well repaired by DNA proofreading enzymes.

A single-crystal X-ray analysis of the synthetic oligomer d(CGCGAATT(epsilon dA)GCG) (epsilon dA = 1,N6-ethenoadenosine) has been carried out. The B-form duplex crystallizes in the orthorhombic space group P2(1)2(1)2(1) with unit cell dimensions a = 24.31 A, b = 39.65 A, and c = 63.05 A. Refinement has converged with R = 0.182 for 2837 reflections in the resolution range 7.0-2.25 A for a model consisting of the duplex, one Mg2+ ion, and 127 water molecules. The structure contains two G.epsilon dA base pairings which adopt a G(anti).epsilon dA(syn) conformation. The geometry of the two mispairs suggests that the G.epsilon dA pairing are held together by three interbase hydrogen bonds. These are N2(G)-H...N1(epsilon dA), N1(G)...N9(epsilon dA), and O6(G)...H-C8(epsilon dA). The last interaction serves to alleviate the destabilizing effect that would occur due to the presence of an unfulfilled hydrogen bond acceptor. A superposition of the G(4).epsilon dA-(21) base pair found in this structure and the Watson-Crick G(4).C(21) base pair observed in the native dodecamer d(CGCGAATTCGCG) indicates a significant difference in the sugar/phosphate backbone. However, the overall conformations of the two duplexes remain similar, suggesting that the modified base pairs are accommodated into the double helix mainly by alterations of the backbone conformation. Such structural rearrangement of the backbone, upon incorporation of epsilon dA, may provide a signal to the 3-methyladenine-DNA glycosylase that repairs such lesions.

The net angle (theta(alpha)) between the seven helical segments of the bacteriorhodopsin (bR) polypeptide and the normal to the membrane plane of the purple membrane (PM) is approximately 0 degrees when determined by oriented far-ultraviolet (UV) circular dichroism (OCD) and midinfrared linear dichroism (IRLD). However, theta(alpha) is approximately 11 degrees when determined by high-resolution electron cryo-microscopy and electron diffraction (EMD). The spectral studies are made with fresh hydrated PM films at ambient temperature, whereas diffraction studies are made with aged glucose-embedded PM at -120 to -268 degrees . The current study presents oriented far-UV OCD results of hydrated PM films embedded with glucose, which can best be interpreted as a change in the magnitude of theta(alpha) (Deltatheta(alpha)) from 0 to 23 degrees as a consequence of glucose embedment. Possible alternative explanations contrary to this conclusion are discussed and ruled out. Therefore, it is suggested that a theta(alpha) of approximately 11 degrees as determined by the EMD method may not be an intrinsic structural characteristic of the native PM but an induced one. The differences in the Deltatheta(alpha) value due to glucose embedment as determined by the two different approaches (23 vs. 11 degrees ) may be attributed to the drastic differences in the experimental conditions used, especially temperature. It is expected that at extremely low temperatures protein dynamics would be highly restricted and Deltatheta(alpha) relatively curtailed. It is concluded that glucose may not be as benign to biological structures as has been assumed in the past.

A current paradigm for visual function centers on the metarhodopsin I (MI) to metarhodopsin II (MII) conformational transition as the trigger for an intracellular enzyme cascade leading to excitation of the retinal rod. We investigated the influences of the membrane lipid composition on this key triggering event in visual signal transduction using flash photolysis techniques. Bovine rhodopsin was combined with various phospholipids to form membrane recombinants in which the lipid acyl chain composition was held constant at that of egg phosphatidylcholine (PC), while the identity of the lipid headgroups was varied. The ratio of MII/MI produced in these recombinants by an actinic flash at 28 degrees C was studied as a function of pH. The results were compared to the photochemical function observed for rhodopsin in native retinal rod outer segment (ROS) membranes, in total native ROS lipid recombinants, and in dimyristoylphosphatidylcholine (DMPC) recombinants. In membrane recombinants incorporating lipids derived from egg PC, as well as in the total ROS lipids control and the native ROS disk membranes, MI and MII were found to coexist in a pH-dependent, acid-base equilibrium on the millisecond time scale. The recombinants of rhodopsin with egg PC, either alone or in combination with egg PC-derived phosphatidylethanolamine (PE) or phosphatidylserine (PS), exhibited substantially reduced photochemical activity at pH 7.0. However, all recombinants comprising phospholipids with unsaturated acyl chains were capable of full native-like MII production at pH 5.0, confirming previous results [Gibson, N.J.. & Brown, M.F. (1990) Biochem. Biophys. Res. Commun. 169, 1028-1034]. It follows that energetic constraints on the MI and MII states imposed by egg PC-derived acyl chains can be offset by increased activity of H+ ions. The data reveal that the major effect of the membrane lipid composition is to alter the apparent pK for the MI-MII conformational equilibrium of rhodopsin [Gibson, N.J., & Brown, M.F. (1991) Biochem. Biophys. Res. Commun. 176, 915-921]. Recombinants containing only phosphocholine headgroups exhibited the lowest apparent pK values, whereas the presence of either 50 mol % PE or 15 mol % PS increased the apparent pK. The inability to obtain full native-like function in recombinants having egg PC-derived chains and a native-like headgroup composition indicates a significant role of the polyunsaturated docosahexaenoic acid (DHA) chains (22:6 omega 3) of the native retinal rod membrane lipids. Temperature studies of the MI-MII transition enabled an investigation of lipid influences on the thermodynamic parameters of a membrane protein conformational change linked directly to function.(ABSTRACT TRUNCATED AT 400 WORDS)

We have investigated the relationship between rhodopsin photochemical function and the retinal rod outer segment (ROS) disk membrane lipid composition using flash photolysis techniques. Bovine rhodopsin was combined with various phospholipids to form recombinant membrane vesicles, in which the lipid acyl chain composition was maintained at that of egg phosphatidylcholine (PC), while the nature of the headgroups was varied. The ratio of metarhodopsin II (MII)/metarhodopsin I (MI) in these recombinants produced by an actinic flash was investigated as a function of pH, and compared with the photochemical activity observed for rhodopsin in native ROS membranes and dimyristoylphosphatidylcholine recombinants. In recombinants made with lipids derived from egg PC, as well as in native ROS membranes, MI and MII were found to be present in a pH-dependent, acid-base equilibrium on the millisecond timescale. The recombinants made with phospholipids containing unsaturated acyl chains were capable of full native-like MII production, but each demonstrated a titration curve with a different pK. In addition, some of the recombinants exhibited apparent deviations from the Henderson-Hasselbalch curve shape. The presence of either phosphatidylethanolamine (PE) or phosphatidylserine (PS) headgroups appeared to increase the amount of MII produced. This may result from alteration of the curvature free energy, in the case of PE, and from the influence of the membrane surface potential in the case of PS. An investigation of the effects of temperature on the MI-MII transition in native ROS membranes and the recombinants was also carried out.(ABSTRACT TRUNCATED AT 250 WORDS)

The conformational dynamic capabilities of the in situ bacteriorhodopsin (bR) can be studied by determination of the changes of the bR net helical segmental tilt angle (the angle between the polypeptide segments and the membrane normal) induced by various perturbations of the purple membrane (PM). The analysis of the far-UV oriented circular dichroism (CD) of the PM provides one means of achieving this. Previous CD studies have indicated that the tilt angle can change from approximately 10 degrees to 39 degrees depending on the perturbants used with no changes in the secondary structure of the bR. A recent study has indicated that the bleaching-induced tilt angle can be enhanced from approximately 24 degrees to 39 degrees by cross-linkage and papain-digestion perturbations which by themselves do not alter the tilt angle. To add further credence, this study has been repeated using midinfrared (IR) linear dichroic spectral analysis. In contrast to the CD method, analysis by the IR method depends on the orientation of the amide plane of the helix assumed. Excellent consistency is achieved between the two methods only when it is assumed that the structural characteristics of the alpha-helices of the bR are equally alpha I and alpha II in nature. Furthermore, the analysis of the IR data becomes essentially independent of the three amide transitions utilized. The net tilt angle of segments completely randomized relative to the incident light must be 54.736 in view of helix symmetry. A value of 54.735 degrees +/- 0.001 degree was achieved by the IR method for the ethanol-treated PM film, establishing this kind of film as an ideal random state standard and demonstrating the accuracy potential of the IR method.

Bovine rhodopsin was recombined with various phospholipids in which the lipid acyl chain composition was held constant at that of egg phosphatidylcholine (PC), while the identity of the headgroups was varied. The ratio of MII/MI produced in the recombinant membrane vesicles by an actinic flash was studied as a function of pH, and compared to the photochemical activity observed for rhodopsin in native ROS membranes. MI and MII were found to coexist in a pH-dependent, acid-base equilibrium on the millisecond timescale. Recombinants made with phospholipids containing unsaturated acyl chains were capable of full native-like MII production, but demonstrated titration curves with different pK values. The presence of phosphoethanolamine or phosphoserine headgroups increased the amount of MII produced. In the case of phosphatidylserine this may result from alteration of the membrane surface potential, leading to an increase in the local H+ activity. The results indicate that the Gibbs free energies of the MI and MII conformational states are influenced by the membrane bilayer environment, suggesting a possible role of lipids in visual excitation.

Rhodopsin in native rod membranes and incorporated into egg phosphatidylcholine (egg PC) vesicles was studied at pH 5 and 7 at 28 degrees C. Rhodopsin function, as monitored by the formation of metarhodopsin II (MII) from metarhodopsin I (MI) following an actinic flash, was found to be largely blocked in egg PC vesicles at pH 7. When the pH was lowered to 5, however, rhodopsin showed essentially equal activity in both native and egg PC membranes. This activity exceeded that found for rhodopsin in native membranes at pH 7. Phospholipid composition is thus shown to directly affect the MI in equilibrium MII equilibrium, which in turn is linked to visual function.

The nature and extent of dehydration-induced molecular structural changes of the purple membrane of Halobacterium halobium have been studied by absorption and circular dichroism spectra in solution and in oriented membrane films. High glycerol concentrations, exhaustive dry nitrogen gas flushing, and exhaustive high-vacuum pumping were employed as dehydrants. The effect of these dehydrants on the spectra were reversible, similar, and additive. Analysis of the spectral changes observed at maximal dehydration revealed: (a) at least two additional optical states of the bacteriorhodopsin, one at higher energy and another at lower energy than the characteristic dark- and light-adapted states; (b) no change in the dichroic ratio at the visible absorption maximum within experimental error; (c) no change in the polarity of the visible monomeric retinylidene circular dichroic bands; (d) pronounced reduction in the characteristic excitonic interactions among the retinals in the hexagonal crystalline lattice of the membrane; (e) no changes in the native structural anisotropism of the membrane in respect to the orientation of the amino acid aromatic rings of the bacteriorhodopsin; (f) no changes in the secondary structure of the bacteriorhodopsin; and (g) a net tilting of approximately 20.5 degrees per segment of the helical polypeptide segments of the bacteriorhodopsin away from the membrane normal. A molecular model of the structural changes of the membrane resulting from water removal consistent with these findings can be constructed. Dehydration results in only subtle localized tertiary structural changes of the protein which do not significantly alter its shape or size. However, there are pronounced global supramolecular structural changes of the membrane. Water removal, which is most likely to be from the lipid headgroups of the membrane, disrupts the interactions responsible for maintaining the native crystalline lattice of the membrane resulting in pronounced randomization of the positions of the proteins in the membrane.

Analysis of the far-ultraviolet solution and the oriented-film circular dichroic (CD) spectra of the purple membrane (PM) has indicated that the alpha-helical segments of its sole protein bacteriorhodopsin (bR) can undergo a significant tilting from the normal to the membrane plane during light-dependent hydroxylamine-mediated bleaching of the bR. However, this drastic change in tertiary structure is free of any observable secondary structural changes. This phenomenon can provide an excellent means for studying the relative contributions of forces responsible for the stability of this transmembrane protein within the membrane bilayer. Perturbation of the PM by varying degrees of papain digestion (resulting in changes in the bR ranging from only an elimination of the long COOH-terminal tail to the additional eliminations of the short NH(2)-terminal tail and a number of linkage amino acids between the helical segments of the bR) and by chemical cross-linking with dimethyl adipimidate (resulting primarily in the formation of intramolecular cross-links) resulted in a significant increase in this bleaching-induced tilting in all cases except the one in which only the COOH-tail was eliminated. The most severe perturbation (2-wk papain digestion) increased the net tilt angle per segment from 24 to 39 degrees with no indication of any secondary structural changes. Although these perturbations drastically reduced the structural stability of the bR to bleaching, they caused virtually no observable changes in the intramolecular structure of the bR or the supramolecular structure of the PM based on analysis of extensive absorption, linear dichroic, and CD spectra. In addition, study of the bleaching rates for the perturbed PM samples indicated that a linear correlation exists between the calculated initial bleaching rates and the net tilt angles.Considering the forces generally assumed to account for the stability of transmembrane proteins in membranes, (a) intersegmental hydrogen bonding and electrostatic interactions, (b) electrostatic interactions between hydrophilic polypeptide segments extending outside the bilayer and the many charged lipid heads of the bilayer, and (c) hydrophobic interactions, it is clear that the results of the bleaching experiments eliminate all but perhaps the last as contributing significantly to the bR stability in the PM. Furthermore, they provide more compelling evidence than previously available that the bR is capable of undergoing relatively large retinyldiene-controlled tertiary structural changes and that the chromophoric retinal serves as the most important factor in the native bR structural stability. This dynamic view of the bR bears directly on models proposed for bR function, favoring those in which protein structural metastability, rather than rigidity, is an essential factor. The proteinquake or deformation wave model proposed by this laboratory falls into this category.