Molecular mechanism by which the nucleoid occlusion factor, SlmA, keeps cytokinesis in check.

In Escherichia coli, cytokinesis is orchestrated by FtsZ, which forms a Z-ring to drive septation. Spatial and temporal control of Z-ring formation is achieved by the Min and nucleoid occlusion (NO) systems. Unlike the well-studied Min system, less is known about the anti-DNA guillotining NO process. Here, we describe studies addressing the molecular mechanism of SlmA (synthetic lethal with a defective Min system)-mediated NO. SlmA contains a TetR-like DNA-binding fold, and chromatin immunoprecipitation analyses show that SlmA-binding sites are dispersed on the chromosome except the Ter region, which segregates immediately before septation. SlmA binds DNA and FtsZ simultaneously, and the SlmA-FtsZ structure reveals that two FtsZ molecules sandwich a SlmA dimer. In this complex, FtsZ can still bind GTP and form protofilaments, but the separated protofilaments are forced into an anti-parallel arrangement. This suggests that SlmA may alter FtsZ polymer assembly. Indeed, electron microscopy data, showing that SlmA-DNA disrupts the formation of normal FtsZ polymers and induces distinct spiral structures, supports this. Thus, the combined data reveal how SlmA derails Z-ring formation at the correct place and time to effect NO.

Chevkinite-Group Minerals from Granulite-Facies Metamorphic Rocks and Associated Pegmatites of East Antarctica and South India

Electron microprobe data are presented for chevkinite-group minerals from granulite-facies rocks and associated pegmatities of the Napier Complex and Mawson Station charnockite in East Antarctica and from the Eastern Ghats, South India. Their compositions conform to the general formula for this group, viz. A(4)BC(2)D(2)Si(4)O(22) where, in the analysed specimens A = (rare-earth elements (REE), Ca, Y, Th), B = Fe(2+) Mg, C = (Al, Mg, Ti, Fe(2+), Fe(3+), Zr) and D = Ti and plot within the perrierite field oftlic total Fe (as FeO) (wt.%) vs. CaO (wt.%) discriminator diagram of Macdonald and Belkin (2002). In contrast to most chevkinite-group minerals, the A site shows unusual enrichment in the MREE and HREE relative to the LREE and Ca. In one sample from the Napier Complex, Y is the dominant cation among the total REE + Y in the A site, the first reported case of Y-dominance in the chevkinite group. The minerals include the most Al-rich yet reported in the chevkinite group (<= 9.15 wt.% Al(2)O(3)), sufficient to fill the C site in two samples. Conversely, the amount of Ti in these samples does not fill the D site. and, thus, some of the Al could be making up the deficiency at D, a situation not previously reported in the chevkinite group. Fe abudances are low, requiring Mg to occupy up to 45% of the B site. The chevkinite-group minerals analysed originated from three distinct parageneses: (1) pegmatites containing hornblende and orthopyroxene or garnet; (2) orthopyroxene-bearing gneiss and granulite; (3) highly aluminous paragneisses in which the associated minerals are relatively magnesian or aluminous. Chevkinite-group minerals from the first two parageneses have relatively high FeO content and low MgO and Al(2)O(3) contents; their compositions plot in the field for mafic and intermediate igneous rocks. In contrast, chevkinite-group minerals from the third paragenesis are notably more aluminous and have greater Mg/Fe ratios.

Characterisation of a Natural Quartz Crystal as a Reference Material for Microanalytical Determination of Ti, Al, Li, Fe, Mn, Ga and Ge

A natural smoky quartz crystal from Shandong province, China, was characterised by laser ablation ICP-MS, electron probe microanalysis (EPMA) and solution ICP-MS to determine the concentration of twenty-four trace and ultra trace elements. Our main focus was on Ti quantification because of the increased use of this element for titanium in- quartz (TitaniQ) thermobarometry. Pieces of a uniform growth zone of 9 mm thickness within the quartz crystal were analysed in four different LA-ICP-MS laboratories, three EPMA laboratories and one solution-ICP-MS laboratory. The results reveal reproducible concentrations of Ti (57 ± 4 lg g-1),Al (154 ± 15 lg g-1), Li (30 ± 2 lg g-1), Fe (2.2 ± 0.3 lg g-1), Mn (0.34 ± 0.04 lg g-1), Ge (1.7 ± 0.2 lg g-1) and Ga (0.020 ± 0.002 lg g-1) and detectable, but less reproducible, concentrations of Be, B, Na, Cu, Zr, Sn and Pb. oncentrations of K, Ca, Sr, Mo, Ag, Sb, Ba and Au were below the limits of detection of all three techniques. The uncertainties on the average concentration determinations by multiple techniques and laboratories for Ti, Al, Li, Fe, Mn, Ga and Ge are low; hence, this quartz can serve as a reference material or a secondary reference material for microanalytical applications involving the quantification of trace elements in quartz.

Major element composition of phenocrysts from the volcanic basement of ODP Hole 125-786B, Izu forearc region, Philippine Sea

Early arc volcanism during Eocene to Oligocene in the Izu forearc region was investigated during ODP Legs 125 and 126 in 1989, and effusive and intrusive volcanics were recovered from Leg 125 Site 786. These rocks were all classified into boninites and associated rocks by Leg 125 Shipboard Scientific Party, and they concluded that boninitic volcanism had occurred before 40 Ma, and arc tholeiitic volcanism began after 40 Ma. In this study, lava flows and breccias that classified into boninite series are divided into two groups, tholeiite and boninite, based on petrographical and petrological properties. Both series are also distinguished by bulk rock composition. It is considered that the sources of both rock types have similar depleted compositions because of their similar, very low bulk HFSE concentrations. We suggest that boninitic and tholeiitic volcanism occurred closely in time and space, and reflected different temperature and water condition.

In-situ Iron isotope measurements and mineral compositions from ODP Hole 206-1256D and IODP Hole 335-U1256D

In-situ Fe isotope measurements have been carried out to estimate the impact of the hydrothermal metamorphic overprint on the Fe isotopic composition of Fe-Ti-oxides and Fe-sulfides of the different lithologies of the drilled rocks from IODP Hole 1256D (eastern equatorial Pacific; 15 Ma crust formed at the East Pacific Rise). Most igneous rocks normally have a very restricted range in their 56Fe/54Fe ratio. In contrast, Fe isotope compositions of hot fluids (> 300 °C) from mid-ocean-ridge spreading centers define a narrow range that is shifted to lower delta 56Fe values by 0.2 per mil - 0.5 per mil as compared to igneous rocks. Therefore, it is expected that mineral phases that contain large amounts of Fe are especially affected by the interaction with a fluid that fractionates Fe isotopes during exsolution/precipitation of those minerals. We have used a femtosecond UV-Laser ablation system to determine mineral 56Fe/54Fe ratios of selected samples with a precision of < 0.1 per mil (2 sigma level) at micrometer-scale. We have found significant variations of the delta 56Fe (IRMM-014) values in the minerals between different samples as well as within samples and mineral grains. The overall observed scale of delta 56Fe (magnetite) in 1256D rocks ranges from - 0.12 to + 0.64 per mil, and of delta 56Fe (ilmenite) from - 0.77 to + 0.01 per mil. Pyrite in the lowermost sheeted dike section is clearly distinguishable from the other investigated lithological units, having positive delta 56Fe values between + 0.29 and + 0.56 per mil, whereas pyrite in the other samples has generally negative delta 56Fe values from - 1.10 to - 0.59 permil. One key observation is that the temperature dependent inter-mineral fractionations of Fe isotopes between magnetite and ilmenite are systematically shifted towards higher values when compared to theoretically expected values, while synthesized, well equilibrated magnetite-ilmenite pairs are compatible with the theoretical predictions. Theoretical considerations including beta-factors of different aqueous Fe-chlorides and Rayleigh-type fractionations in the presence of a hydrous, chlorine-bearing fluid can explain this observation. The disagreement between observed and theoretical equilibrium fractionation, the fact that magnetite, in contrast to ilmenite shows a slight downhole trend in the delta 56Fe values, and the observation of small scale heterogeneities within single mineral grains imply that a general re-equilibration of the magnetite-ilmenite pairs is overprinted by kinetic fractionation effects, caused by the interaction of magnetite/ilmenite with hydrothermal fluids penetrating the upper oceanic crust during cooling, or incomplete re-equilibration at low temperatures. Furthermore, the observation of significant small-scale variations in the 56Fe/54Fe ratios of single minerals in this study highlights the importance of high spatial-resolution-analyses of stable isotope ratios for further investigations.

Magnetic properties, grain sizes and minerals at DSDP Site 83-504B

Twenty-seven samples from the Leg 83 section of Hole 504B have been investigated using magnetic, optical, and electron optical methods. The primary magnetic mineral to crystallize was titanomagnetite of approximate composition Fe2.4Ti0.6O4 (TM60), but none survives, nor is there evidence of titanomaghemite produced by oxidation of TM60. The average measured magnetic properties can be interpreted in terms of magnetite, Fe3O4, having average grain size of <1 µm and present in average volume concentration of - 0.5%. The intensity of the natural remanent magnetization (NRM) of the rocks could also be accounted for as being a thermoremanence carried by this mineral. Although the heterogeneity of the titanomagnetite grains could be detected optically, the texture of the intergrown phases is poorly developed. In some samples from the massive units of the lower part of the section, trellis patterns were visible. The Fe3O4 present in the intergrowths is too intimately mixed with the other intergrown phases to be revealed by electron microprobe analysis that simply returns the bulk composition of the intergrowth (oxidized TM60). The path by which the mineral assemblage evolved from TM60 to an Fe304-containing intergrowth, under the temperature and pressure conditions obtaining in the Leg 83 section, makes interesting speculation. Deuteric oxidation, maghemitization/inversion, or some hypothetical low-temperature/high-pressure oxidation by a leaching-of-iron process may all play roles.

Petrology and geochemistry of peridotites from IODP Site 304-U1309

Peridotite samples recovered from IODP Site U1309 at the Atlantis Massif in the Mid-Atlantic Ridge were examined to understand magmatic processes for the oceanic core complex formation. Original peridotite was fragmented, and the limited short peridotite intervals are now surrounded by a huge gabbro body probably formed by late-stage melt injections. Each peridotite interval has various petrographical and geochemical features. A spinel harzburgite in contact with gabbro shows evidence of limited melt penetrations causing gradual compositional change, in terms of trace-element compositions of pyroxenes, as well as modal change near the boundary. Geochemistry of clinopyroxenes with least melt effects indicates that the harzburgite is originally mantle residue formed by partial melting under polybaric conditions, and that such a depleted peridotite is one of the components of the oceanic core complex. Some of plagioclase-bearing peridotites, on the other hand, have more complicated origin. Although their original features were partly overprinted by the injected melt, the original peridotites, both residual and non-residual materials, were possibly derived from the upper mantle. This suggests that the melt injected around an upper mantle region or into mantle material fragments. The injected melt was possibly generated at the ridge-segment center and, then, moved and evolved toward the segment end beneath the oceanic core complex.

Chemistry of various minerals of altered basalts from ODP Hole 111-504B

Basalts recovered from Hole 504B during ODP Leg 111 are more or less altered, but there is no sign of strong shear stress or widespread penetrative deformation; hence, they retain well their primary (igneous) structures and textures. The effect of alteration is recognized as the partial or total replacement of primary minerals (olivine, clinopyroxene, and plagioclase) by secondary minerals and as the development of secondary minerals in open spaces (e.g., veins, fractures, vugs, or breccia matrix). The secondary minerals include zeolite (laumontite and stilbite), prehnite, chlorite, epidote, Plagioclase (albite and/or oligoclase), amphibole (anthophyllite, cummingtonite, actinolite, and hornblende), sodic augite, sphene, talc, anhydrite, chalcopyrite, pyrite, Fe-Ti oxide, and quartz. Selected secondary minerals from several tens of samples were analyzed by means of an electron-probe microanalyzer; the results are presented along with brief considerations of their compositional features. In terms of the model basaltic system, the following two types of low-variance (three-phase) mineral assemblages were observed: prehnite-epidote-laumontite and prehnite-actinolite-epidote; both include chlorite, albite and/or oligoclase, sphene, and quartz. The mineral parageneses delineated by these low-variance mineral assemblages suggest that the metamorphic grade ranges from the zeolite facies to the prehnite-actinolite facies. The common occurrence of prehnite indicates that greenschist facies conditions were not attained even in the deepest level of Hole 504B, which, in a strict sense, contradicts the previous interpretation that the lower portion of Hole 504B suffered greenschist facies alteration.

Geochemistry of Qeqertaa xenoliths

This study presents electron microprobe data for dunite xenoliths from a lamprophyre dyke located on the island of Qeqertaa, West Greenland. The minimum age of this dyke is Palaeoproterozoic and it experienced amphibolite facies metamorphism and deformation during that era. The samples consist of nearly 200 xenoliths with a size range of 0.5-8 cm. These dunite xenoliths have olivine Mg#, that range from 80.3 to 94.6 (n = 579) with a mean of 92.6. Orthopyroxene is found in three xenoliths and garnet in five others. The latter suggests the depth of the Qeqertaa xenolith suite to be near the diamond stability-field, which is substantiated by the finding of diamonds in bulk samples of the Qeqertaa dyke. This further indicates the presence of a lithospheric mantle domain dominated by high-Mg# dunite to this depth in Palaeoproterozoic time. Cr-rich spinel, in the 0.1-0.2 mm size range, is found within and between olivine grains in individual xenoliths. These Cr-spinels yield Fe-Mg exchange temperatures of 400-600°C. However, the presence of intermediate spinel compositions spanning the lower temperature solvus suggests that equilibration temperatures were >550°C. Fe3+#, expressed as 100xFe3+/(Fe3++Al+Cr)), is shown to be a useful parameter in order to screen for altered spinel (Fe3+#>10) with disturbed Mg# and Cr#. The screened spinel data (Fe3+#<10) show a distinctly different trend in terms of spinel Cr# versus Mg#, compared to unmetamorphosed xenoliths in Tertiary lavas and dikes from Ubekendt Ejland and Wiedemann Fjord, respectively, also located within the North Atlantic craton. This difference likely reflects amphibolite facies metamorphic resetting of the Qeqertaa xenolith suite by Fe-Mg exchange. Given the similarity of the Qeqertaa xenolith suite with the Ubekendt and Wiedemann suites, in terms of their olivine Mg# and spinel Cr# distribution, high-Mg# dunite is likely to be an important component of the subcontinental lithospheric mantle beneath the North Atlantic craton and appears to have spanned a vertical distance of at least 150 km in this region, even during the Palaeoproterozoic.

Geochemistry of ash and pumice of ODP Hole 132-810C

Air-fall volcanic ash and pumice were recovered from 22 intervals in upper Miocene-Pleistocene nannofossil oozes cored in Hole 810C on Shatsky Rise, northwest Pacific. Shatsky Rise is near the eastern limit of ash falls produced by explosive volcanism in arc systems in northern Japan and the Kuriles, more than 1600 km away. Electron probe analyses establish that the ash beds and pumice pebbles are andesitic to rhyolitic in composition, and belong to both tholeiitic and high-alumina lineages similar to tephra from Japanese volcanoes. High-speed winds in the polar-front and subtropical jets are evidently what propelled the ash for such a distance. The pumice arrived by flotation, driven from the same directions by winds, waves, and currents. It is not ice-rafted debris from the north. One thick pumice bed probably was deposited when a large pumice mat passed over Shatsky Rise. Far more abundant ash occurs in sediments cored at DSDP Sites 578 through 580, about 500 km west of Shatsky Rise. Most of the ash and pumice at Shatsky Rise can be correlated with specific ash beds at 1, 2, or all 3 of these sites by interpolating to precisely determined magnetic reversal sequences in the cores. Most of the correlations are to thick ash layers (5.7 +/- 3.0 cm) at one or more sites. These must represent extremely large eruptions that spread ash over very wide areas. Whereas several of the thicker correlative ashes fell from elongate east-trending plumes directed from central Japan, the majority of them - dating from about 2 Ma - came from the North Honshu and Kurile arc systems to the northwest. This direction probably was in response to both long-term and seasonal fluctuations in the location and velocity of the polar-front jet, and to more vigorous winter storm fronts originating over glaciated Siberia.

Geochemistry of glass shards in the volcanic ash layers of the Izu-Bonin Arc

To examine the processes and histories of arc volcanism and of volcanism associated with backarc rifting. 130 samples containing igneous glass shards were taken from the Plioccne-Quatemai^ succession on the rift Hank (Site 788) and the Quaternary fill in the basin fill of the Sumisu Rift (Sites 790 and 791). These samples were subsequently analyzed at the University of Illinois at Chicago and Shizuoka University. The oxides determined by electron probe do not account for the total weight of the material; differences between summed oxides and 100% arise from the water contents, probably augmented by minor losses thai result from alkali vaporization during analysis. Weight losses in colorless glasses are up to 9%; those in brown glasses (dacitcs to basalts) arc no more than 4.5%; shards from the rift-flank (possibly caused by prolonged proximity to ihc scafloor) generally have higher values than those from the rift-basin fill How much of the lost water is magmatic, and how much is hydrated is uncertain; however, although the shards absorb potassium, calcium, and magnesium during hydration in the deep sea, they do so only to a minor extent that does not significantly alter their major element compositions. Therefore, the electron-probe results are useful in evaluating the magmatism recorded by the shards. Pre- and syn-rift Izu-Bonin volcanism were overwhelmingly dominated by rhyolile explosions, demonstrating that island arcs may experience significant silicic volcanism in addition to the extensive basaltic and basaltic andestic activity, documented in many arcs since the 1970s, that occurs in conjunction with the andesitic volcanism formerly thought to be dominant. Andesitic eruptions also occurred before rifting, but the andesitic component in our samples is minor. All the pre- and syn-rift rhyolites and andesites belong to the low-alkali island-arc tholeiitic suite, and contrast markedly with the alkali products of Holocene volcanism on the northernmost Mariana Arc that have been attributed to nascent rifting. The Quaternary dacites and andesites atop the rift flank and in the rift-basin fill are more potassic than those of Pliocene age, as a result of assimilation from the upper arc crust, or from variations in degrees of partial melting of the source magmas, or from metasomatic fluids. All the glass layers from the rift-flank samples belong to low-K arc-tholeiitic suites. Half of those in the Pliocene succession are exclusively rhyolitic: the others contain minor admixtures of dacite and andesite, or andesite and either basaltic andesite or basalt. In Contrast, the Quaternary (syn-rift) volcaniclastics atop the rift-flank lack basalt and basaltic andesite shards. These youngest sediments of the rift flank show close compositional affinities with five thick layers of coarse, rhyolitic pumice deposits in the basin fill, the two oldest more silicic than the younger ones. The coarse layers, and most thin ash layers that occur in hemipelagites below and intercalated between them, are low-K rhyolites and therefore probably came from sources in the arc. However, several thin rhyolitic ash beds in the hemipelagites are abnormally enriched in potassium and must have been provided by more distal sources, most likely to the west in Japan. Remarkably, the Pliocene-Pleistocene geochemistry of the volcanic front does not appear to have been influenced by the syn-rift basaltic volcanism only a few kilometers away. Rare, thin layers of basaltic ash near the bases of the rift-basin successions are not derived from the arc. They deviate strongly from trends that the arc-derived glasses display on oxide-oxide plots, and show close affinities to the basalts empted all over the Sumisu Rift during rifting. These basalts, and the basaltic ashes in the basal rift-basin fill, arc compositionally similar to those erupted from mature backarc basins elsewhere.

Chemistry of primary and secondary phases in intraplate basalts and volcaniclastic sediments at DSDP Leg 89 Holes

Electron microprobe data are presented for clinopyroxenes, plagioclases, palagonites, smectites, celadonites, and zeolites in Hole 462A sheet-flow basalts and Site 585 volcaniclastic sediments. Glomerocrystic clinopyroxenes in Hole 462A are predominantly Ti-poor augites with minor fractionation to ferroaugites in rim portions. Quenched plumose clinopyroxenes show considerable variation from Ca-rich to Ca-poor augites, although all are characterized by being Tirich and Cr-poor relative to the glomerocrysts. Two differentiated series of Site 585 pyroxene compositions, calcic augite and diopside-salite, demonstrate the coexistence, in the vitric and lithic clasts, of tholeiitic and alkali basalt types, respectively. Plagioclase compositions in all samples are mainly labradorites, although some zoned Hole 462A glomerocrysts range from An73 to An20 and are characterized by high Mg and Fe contents in the more calcic varieties. The K content of the plagioclases is highest in the more sodic crystals, although the overall higher orthoclase component of Site 585 plagioclases reflects the generally higher bulk-rock K content. The compositions of both secondary smectites and celadonites are similar irrespective of the alteration location (glass, matrix, vesicles, etc.), although brown smectites replacing interstitial glass have marginally higher total Fe contents than pale green and yellow smectites. Analyzed zeolites are mainly phillipsites with variable alkali content, and, together with associated celadonite, represent late-stage alteration repositories for K under mildly oxidizing conditions. The compositions of both early and late secondary minerals are typical of those formed by the submarine alteration of basaltic rocks at low temperatures.

Description and geochemical composition of tephra layers from ODP Hole 186-1150A and Site 186-1151

The sediments collected at Sites 1150 and 1151 during Leg 186 included many tephra layers and volcaniclastic detritus. In order to identify these tephras, the major oxide compositions of individual glass shards were determined by electron probe microanalyzer. The uppermost four tephras in sediments from Hole 1150A are correlated with the Towada-Hachinohe tephra (To-H; Tohoku district), Shikotsu Daiichi (1st) tephra (Spfa-1; Hokkaido district), Narugo-Yanagisawa tephra (Nr-Y; Tohoku district), and Aso-4 tephra (Kyushu district), respectively. The uppermost tephra in Hole 1151C is correlated with To-H tephra. To-H, Spfa-1, and Aso-4 tephras are also present in piston core KH94-3, LM-8, collected between Sites 1150 and 1151. Eruptive ages of To-H and Spfa-1 estimated from the oxygen isotopic Stages of core KH94-3, LM-8 are between 14.9-15.3 and 39.5-40.1 ka.

The nucleoporin Nup98 associates with the intranuclear filamentous protein network of TPR

The Nup98 gene codes for several alternatively spliced protein precursors. Two in vitro translated and autoproteolytically cleaved precursors yielded heterodimers of Nup98-6kDa peptide and Nup98-Nup96. TPR (translocated promoter region) is a protein that forms filamentous structures extending from nuclear pore complexes (NPCs) to intranuclear sites. We found that in vitro translated TPR bound to in vitro translated Nup98 and, via Nup98, to Nup96. Double-immunofluorescence microscopy with antibodies to TPR and Nup98 showed colocalization. In confocal sections the nucleolus itself was only weakly stained but there was intensive perinucleolar staining. Striking spike-like structures emanated from this perinucleolar ring and attenuated into thinner structures as they extended to the nuclear periphery. This characteristic staining pattern of the TPR network was considerably enhanced when a myc-tagged pyruvate kinase-6kDa fusion protein was overexpressed in HeLa cells. Double-immunoelectron microscopy of these cells using anti-myc and anti-TPR antibodies and secondary gold-coupled antibodies yielded row-like arrangements of gold particles. Taken together, the immunolocalization data support previous electron microscopical data, suggesting that TPR forms filaments that extend from the NPC to the nucleolus. We discuss the possible implications of the association of Nup98 with this intranuclear TPR network for an intranuclear phase of transport.

Intrasarcomere [Ca2+] gradients in ventricular myocytes revealed by high speed digital imaging microscopy.

Cardiac muscle contraction is triggered by a small and brief Ca2+ entry across the t-tubular membranes, which is believed to be locally amplified by release of Ca2+ from the adjacent junctional sarcoplasmic reticulum (SR). As Ca2+ diffusion is thought to be markedly attenuated in cells, it has been predicted that significant intrasarcomeric [Ca2+] gradients should exist during activation. To directly test for this, we measured [Ca2+] distribution in single cardiac myocytes using fluorescent [Ca2+] indicators and high speed, three-dimensional digital imaging microscopy and image deconvolution techniques. Steep cytosolic [Ca2+] gradients from the t-tubule region to the center of the sarcomere developed during the first 15 ms of systole. The steepness of these [Ca2+] gradients varied with treatments that altered Ca2+ release from internal stores. Electron probe microanalysis revealed a loss of Ca2+ from the junctional SR and an accumulation, principally in the A-band during activation. We propose that the prolonged existence of [Ca2+] gradients within the sarcomere reflects the relatively long period of Ca2+ release from the SR, the localization of Ca2+ binding sites and Ca2+ sinks remote from sites of release, and diffusion limitations within the sarcomere. The large [Ca2+] transient near the t-tubular/ junctional SR membranes is postulated to explain numerous features of excitation-contraction coupling in cardiac muscle.