A reconsideration of cf. Psilophyton princeps (Croft & Lang, 1942), a zosterophyll widespread in the Lower Old Red Sandstone of South Wales

EE WARDS, D., KENRICK, P. & CARLUCCIO, L. M., 1988. A reconsideration of cf. P lophyton princeps (Croft & Lang, 1942), a zosterophyll widespread in the Lower Old Rt 1 Sandstone of South Wales. The Lower Devonian plant from Llanover Quarry, Gwent, cal ed cf. Psilophyton princeps , is shown to be a zosterophyll and placed in a new genus. It comprises an ere t planar pseudomonopodial and isotomously branching system of spiny axes with subaxillary pre ections (axillary tubercles) with circinate tips, sometimes replaced by a downwardly directed, spiring, branching axis. Its xylem, strap-shaped in cross-section and exarch, is composed of directly and ndirectly connected annular thickenings. An extended distal fertile zone consists of axes with spot ingia in two opposite or sub-opposite rows. Each sporangium comprises two equal valves, ellip'ical to reniform in face view, and is held upright on a short curved stalk. Dehiscence is around the convex margin which is bordered by a narrow strip of thickening. The Welsh plants are comp ired with other zosterophylls and appear closest to Sawdonia ornata except that they possess sub-axillay branches and lack the characteristic dark-tipped spines. Detailed analysis of coalified mater: and the distribution and fabric of pyrite in permineralizations shows that the original structure of the tracheids was similar to that in Gosslingia and most other zosterophylls, and that the taphonomic processes, with lignified walls preserved as coalified layers and softer tissues replaced by pyrite, were also broadly the same. Permineralizations in pyrite and limonite allow an evaluation of the effects of oxidation of pyrite on original cell structure.     

Crystallography of hemerythrin

X-ray crystallographic studies of hemerythrin from Golfingia gouldii show that the molecules pack in a tetragonal cell with two sets of molecules in an apparently face-centred array seen in projection along the 4-fold axis, but displaced relatively to each other by approximately $\text{c}\text{10}$ in the axial direction. Both sets of molecules lie on 4-fold rotation axes, so that the subunits of each octameric molecule are related in pairs by a molecular 4-fold rotation axis. The two subunits of each pair are probably related by non-crystallographic 2-fold rotation axes perpendicular to the 4-fold axes and lying at 10 ° and 55 ° to the a and b axes. At low resolution the subunits are apparently arranged approximately in the form of a square prism. Along each 4-fold crystallographic axis there are two hemerythrin molecules, nearly equidistant and having similar but not identical orientations.     

A tetragonal crystal form of horse spleen apoferritin and its relationship to the cubic modification

Horse spleen apoferritin has been crystallized as tetragonal plates and needles with a unit cell with $\text{a = b = 147 ± 0.5}\text{A}\text{?}\text{and}\text{c = 154.4 ± 0.5}\text{A}\text{?}$. The space group is P42₁2 and the unit cell contains two molecules in a pseudo-body-centred arrangement. The intensity distributions and calculated rotation functions of tetragonal and cubic crystals have been compared. The symmetry of the diffraction patterns from cubic crystals indicates that the molecules have 432 symmetry with their 4-fold axes lying along the cube axes. In the tetragonal crystals one molecular 4-fold axis lies parallel to c, the unique axis, while the rest of the molecular point symmetry is not used by the lattice. Instead the remaining 4-fold axes of the two molecules, which lie in planes perpendicular to c, are rotated ± 17.5 ° with respect to the tetragonal a axis. The finding that apoferritin reassembled from subunits can be crystallized in both tetragonal and cubic forms confirms its conformational similarity to native molecules.     

Unit cell transormations in yeast phenylalanine transfer RNA crystals

The orthorhombic unit cell of crystalline yeast phenylalanine transfer RNA has dimensions $\text{a = 33}\text{A}\text{?}$, $\text{b = 56}\text{A}\text{?}$ and $\text{c = 161}\text{A}\text{?}$. When the mother liquor dries partially, a series of transformations takes place in which the a and b axes change very little but the c axis decreases abruptly first to 128 Å and then to 109 Å. In a closely related orthorhombic cell in a different space group the c axis is 104 Å. Although there is some loss in resolution in these smaller unit cells, the over-all distribution of scattering intensity does not change substantially. This suggests that the tRNA molecules can slide together along the c axis without a substantial change in internal structure.     

The conformation and orientation of copper(II)-bleomycin intercalated with DNA

EPR data are used to describe the conformation and identity of the atoms coordinated to Cu(II) in Cu(II)-bleomycin bound to oriented DNA fibers. The fibers were slowly drawn from viscous solutions of Cu(II)-bleomycin-DNA containing one Cu(II)-bleomycin to 200 basepairs. EPR measurements were made at room temperature and 90 K for different orientations of the external magnetic field with respect to the helical axes of the fibers. The g-values ($\text{g}{}_{\mathrm{}}\text{=2.21}$, g_⊥ =2.04) and the hyperfine constant ($\text{A}{}_{\mathrm{}}\text{=175}\text{G}$) are consistent with values expected for Cu(II) chelated to a square planar array of ligands. In the oriented fibers, the square planar arrays do not all have the same orientations with respect to the fiber axes. At room temperature the chelated ions have rotational freedom in which the normal to the planar array has almost complete freedom of rotation about axes perpendicular to the DNA fiber axes. The normal maintains an angle of 75° with respect to the axis, in the plane of the basepair, about which it rotates. Nine superhyperfine peaks on the high field side of the EPR spectrum were partially resolved. The number and splitting (12 G) of these superhyperfine peaks indicate that four nitrogen atoms are chelated to Cu(II) in a square planar array. These data on Cu(II)-bleomycin bound to DNA give information on the orientation of the metal-containing portion of bleomycin which lies outside the double helix.     

Ribosomal proteins L1, L17 and L27 from Escherichia coli localized at single sites on the large subunit by immune electron microscopy

Three-dimensional locations have been determined for Escherichia coli ribosomal proteins L1, L17 and L27 by immune electron microscopy using antibodies directed against these proteins. From the positions of immunoglobulin G attachment, observed in two characteristic projections, it was determined that these three proteins are located at single sites in different regions on the surface of the large subunit. In the quasisymmetric projection, L1 maps on the side opposite the “$\text{L}\text{7}\text{L}\text{12}$ stalk,” named the L1 ridge; protein L17 maps at the base of the subunit opposite the “central protuberance” (toward the $\text{L}\text{7}\text{L}\text{12}$ side of the subunit); and protein L27 is found on the central protuberance (on the side distal to the $\text{L}\text{7}\text{L}\text{12}$ stalk). In the asymmetric projection, proteins L1 and L27 are found on the surface of the subunit contracting the small subunit and protein L17 is on the surface of the subunit distal to the small subunit; i.e. on the cytoplasmic surface of the large subunit. Antibody binding at all three sites was eliminated when the immunoglobulin G molecules were preabsorbed with their specific proteins.     

Insect wax secretion the growth of tubular crystals

Filaments of a pure long-chain wax secreted by the wooly alder aphid are shown to represent a previously-uncharacterized, tubular, crystal habit for paraffins. Although this habit is never seen in solution or epitaxial growth of such materials, it requires only a circular closure at the wax secretion site, further growth behavior being controlled totally by van der Waal's intermolecular interactions. The linear paraffin-like wax molecules pack in the filament monolayer envelope with chain axes oriented radially from the filament axis. Elongation of the wax filaments corresponds to the strong interactions along the [110] vectors in the O_⊥ polymethylene chain packing, and stabilization of the filament occurs via strong interchain interactions along $\text{[1}\text{1}\text{0]}$ and [010] in helical paths of opposite chirality.     

The crystal structure of cholesteryl dihydrogen phosphate

Crystals of cholesteryl dihydrogen phosphate grown from 1,4-dioxane solution are monoclinic, space group C2 with $\text{a = 24.40, b = 6.27, c = 40.86}\text{A}\text{?}\text{and}\text{β = 102.7°}$. The asymmetric unit contains two molecules of cholesteryl phosphate CP and one dioxane molecule of the solvent. The CP molecules pack tail to tail in a bilayer structure. Within the layer they are arranged in double rows with their phosphate groups linked to ribbons by hydrogen bonds. Laterally the double strands of phosphate groups are separated by rows of dioxane molecules. The dioxane serves as hydrogen bond acceptor and as a spacer molecule that compensates the differences in cross-sectional area of the cholesteryl residue (38.4 Ų and the phosphate group (24 Ų). In the cholesterol matrix the CP molecules joined to double rows have packing contact with the smooth side of their skeleta and interdigitate with their annular methyl groups with those of molecules of the adjacent double rows. The branched cholesteryl side chains facing the bilayer center are loosely packed and show considerable disorder and/or thermal motion.     

Sequence regularities and packing of collagen molecules

Fourier analysis of sequences along edges of the type I collagen molecule constructed from two α1(I) and one α2 chains shows that the molecule is two-sided if the supercoil pitch of the α chains along the molecular axis, P, is 39 residues ($\text{D}\text{6}$, where D = 234 residues or 67 nm). One side has alternating charged and hydrophobic regions with spacings of $\text{D}\text{6}$, while the other side has an excess of hydrophobic residues with a spacing of $\text{D}\text{11}$. These characteristics arise from sequence regularities in the α chains and the geometric relationship between the chains. The pattern is marginally strongest with α2 as chain 1. The $\text{D}\text{6}$ sides could form the inside of a helical microfibril where contacts between molecules would fall P apart along the α chains. The $\text{D}\text{11}$ sides could form the outside of the microfibril where contacts between microfibrils would be spaced apart by the α chain supercoil along the microfibril axis, P′. If the microfibril is a 5₄ helix of D-staggered collagen molecules with a left-handed supercoil of pitch $\text{20D}\text{11}$, P′ is close to $\text{2D}\text{11}$ (43 residues). $\text{2D}\text{11}$ subsets in the α chains give rise to the $\text{D}\text{11}$ spacing along the molecule. The microfibril has 4₁ screw symmetry satisfying X-ray diffraction evidence that microfibrils pack in a tetragonal unit cell.This model is the same as proposed previously by us (Trus & Piez, 1976: Piez & Trus, 1977) except that P = 39 rather than 30 residues. Contrary to our earlier assumption, P = 39 residues is within the range allowed by X-ray diffraction measurements. The present results favor P = 39 since it relates regularities in the α chain sequences to helical parameters in a direct way. Furthermore, model studies show that geometric arguments which support P = 30 are equally strong at P = 39 residues.     

Interactions and space requirement of the phosphate head group of membrane lipids: The single crystal structures of a triclinic and a monoclinic form of hexadecyl-2-deoxyglycerophosphoric acid monohydrate

The crystal structures of a triclinic form (HPA1) and a monoclinic form (HPA2) of hexadecyl-2-deoxyglycerophosphoric acid monohydrate were determined by single crystal analysis. The unit cell dimensions for HPA1 are $\text{a = 4.75, b = 5.72, c = 44.36}\text{A}\text{?}$ and α = 91.0, β = 101.5, γ = 100.5° (P$\text{1}$) and for HPA2, $\text{a = 4.75, b = 5.72, c = 88.72}\text{A}\text{?}$ and γ = 100.8° (P2₁). In both structures the molecules are fully extended and pack tail-to-tail in bilayers with tilting (47°) hydrocarbon chains. In HPA2, however, the chain tilt alternatingly changes direction in adjacent bilayers, giving rise to a doubled unit cell which spans two bilayers. The dihydrogen phosphate groups interact by hydrogen bonds and are arranged in rows. Laterally between these phosphate rows the water molecules are accommodated producing a compact two-dimensional network of hydrogen bonds. The packing cross-section in the layer plane of the dihydrogen phosphate monohydrate group is 26.7 Ų in both structures. The hydrocarbon chains pack according to the triclinic (T|) chain packing mode. In HPA2, however, the chain packing is somewhat less compact with accounts for a 2% increase in the molecular volume. In both structures the ether oxygen is accommodated into the hydrocarbon matrix without distortion of the chain packing.     

Hyaluronic acid: a double-helical structure in the presence of potassium at low pH and found also with the cations ammonium, rubidium and caesium.

An anti-parallel double-helical structure is proposed for hyaluronic acid in the presence of the cations K ⁺, NH⁺₄, Rb⁺ and Cs⁺. In particular the crystalline phase containing potassium ions, and in a defined pH range, has been determined and refined against the X-ray diffraction amplitudes. The reflections in the diffraction pattern index on a tetragonal unit cell (a = b = 1.714 nm, c (fibre axis) = 3.28 nm) with observed systematic absences of the form h + k + l = 2n for general hkl reflections and l = 4n (where n is an integer) for 001 reflections. Two double-helical molecules pass through the unit cell at positions ($\text{1}\text{4}\text{,}\text{1}\text{4}\text{, 0}$) and ($\text{3}\text{4}\text{,}\text{3}\text{4}\text{, 0}$) as defined by space group I4₁22. Each chain forms a contracted (axial advance per disaccharide repeat of 0.82 nm) 4-fold left-handed helix which intertwines with a neighbouring chain of opposite polarity about a common axis. Features of the structure are the positioning of the carboxyl group toward the core of the double helix and the presence of hydrophobic and hydrophilic pockets between adjacent double helices. The state of protonation of the hyaluronate molecule is discussed in the light of the infrared evidence. Common physicochemical features of these four cations which promote this particular doublehelical conformation for hyaluronate are considered.     

Peridermal cell patterning in the feather-forming skin of the chick embryo

The shape, distribution, and orientation of peridermal cells were examined in the dorsolumbar skin of $\text{7}\text{1}\text{2}\text{-}\text{day}$ chick embryos. Most feather rudiments of middorsal and lateral rows showed a marked cephalocaudal polarity. A similar polarity was found in the prospective rudiments of skin areas lateral to the last-formed row. On the cranial slope and apex of rudiments, cells are convex and predominantly elongated at right angles with respect to the cephalocaudal axis, whereas on the caudal slope, most cells are flat, polygonal, surrounded by a border-line ridge, and oriented predominantly with their long axis parallel to the cephalocaudal axis. The significance of this pattern is discussed in view of the fact that the epidermis is the determinant tissue in feather orientation.     

Structure of Panulirus interruptus hemocyanin at 5 Å resolution

The hemocyanin from the spiny lobster Panulirus interruptus, a hexamer with a molecular weight of approximately 540,000, was crystallized in space group P2₁ with two molecules in the unit cell and cell dimensions $\text{a = 119.8}\text{A}\text{?}\text{, b = 193.1}\text{A}\text{?}\text{, c = 122.2}\text{A}\text{?}\text{and}\text{β = 118.1 °}$. With screened precession photographs a three-dimensional set of reflections was collected up to 10 Å resolution. Both the conventional and the fast rotation function programs were applied and gave results that were in excellent agreement with each other. The hemocyanin hexamer has 32 point group symmetry. Its 3-fold molecular axis runs approximately parallel to the crystallographic 2-fold screw axis.X-ray diffraction data to 5 Å resolution were collected by the oscillation method. Rotation function studies with data between 7 and 5 Å resolution confirmed the 10 Å studies and, furthermore, showed that the rotation axes relating subunits within one hexameric molecule can be distinguished from the rotation axes relating subunits belonging to different hexamers in the unit cell. The local 3-fold axis in the hexamer makes an angle of about 6 ° with the crystallographic 2-fold screw axis.For a mercury and a platinum derivative three-dimensional data sets were collected to 5 Å by the oscillation method. The difference Patterson of the platinum derivative could be solved. The eventual number of heavy-atom sites was 36 for the platinum derivative and 70 for the mercury derivative. From the well-occupied sites the point-group symmetry of the molecule could be established accurately. In addition, the centre of the hexamer could be located within 0.2 Å.Protein phases were obtained from isomorphous as well as anomalous differences. A “best” electron density map calculated with these phases showed the shape of the hexameric molecule as well as the boundaries of the six subunits. Correlation coefficients between the densities of the subunits showed little variation, suggesting a random distribution of the different subunit types (Van Eerd & Folkerts, 1981) over the six positions in the hexamer.The subunits are positioned at the corner of an antiprism. When viewed along the 3-fold axis the hexamer is roughly hexagonal in shape, with a diameter of approximately 120 Å. Viewed along one of the 2-fold axes the molecule is of rectangular shape with dimensions 95 Å × 120 Å. The subunit can be described as an ellipsoid of irregular shape with axes of 80 Å, 55 Å and 48 Å. Each subunit makes extensive contacts with three other subunits in the hexamer and, possibly, a much weaker contact with a fourth subunit.     

CRENATICAULIS,A NEW GENUS OF DEVONIAN PLANTS ALLIED TO ZOSTEROPHYLLUM,AND ITS BEARING ON THE CLASSIFICATION OF EARLY LAND PLANTS

The name Crenaticaulis verruculosus is proposed for slender, pseudomonopodially and dichoto-mously branching plants that bore opposite to subopposite sporangia along the stem and two rows of prominent, multicellular teeth on opposite sides of the terete axis. Epidermal cells were either narrow and elongate parallel to the stem or short with a papillate outer tangential wall. Axillary tubercles were present on one side of the stem near lateral branches. Some tubercles bore remnants of branches. Sporangia dehisced along their distal margins into two unequal halves. No spores were found. Occasional short lengths of stem were petrified by iron pyrite. Sections revealed a cortex consisting of four to six rows of thick-walled cells and a xylem strand. The strand was elliptical in transverse section and maturation was exarch. Tracheids were chiefly scalariform. It is suggested that the so-called axillary tubercles, known in several plants of Devonian age, were scars of rhizophores like those in the modern genus Selaginella. The plant is referred to the subdivision Zosterophyllophytina.     

Comparison of mammalian collagen and elasmobranch elastoidin fiber structures, based on electron density profiles.

Standard difference-Fourier methods of crystallography, applied to the axial small-angle X-ray diffraction of elastoidin, develop a four-strip model for the distribution of electron density along shark-fin ceratotrichial axes. This result is obtained directly from X-ray data. The model consists of three major strips with centers separated approximately by $\text{d}\text{3}$ ($\text{d = 670}\text{A}\text{?}$, the familiar collagen macroperiod), superimposed upon a wide strip extending over 0·49 d, representing the overlap-hole zone background, also found in mammalian collagens. The three narrower strips correspond to cross-sections which resist negative staining or diametral contraction on drying, reported to be characteristic of elastoidin from electron microscopy. Chemical evidence suggests that these unique cross-sections (“superbands”) occur at axial locations where a tyrosine-rich matrix, intimately associated with very thin collagen units, produces paracrystalline order with good axial registration but poor transverse order, across an entire ceratotrichium (diam. ~ 1 to 2 mm). The analogous but quite different condition in mammalian collagen fibers involves an intra-fibrillar paracrystalline order (diam. approx. 1000 Å), with inter-fibrillar stabilization by a mucopolysaccharide matrix. Stiffening of the elastoidin by means of the tyrosine-rich matrix exemplifies a way, alternative to mineralization processes (e.g. in bone), of reducing collagenous fiber flexibility.     

The crystalline structure of collagen fibrils in tendon.

New data have been collected on the crystalline structure of collagen fibrils in tendon. The unit cell in decrimped tendon has been determined by measurements of the Bragg reflections in the X-ray diffraction pattern. The results are consistent with a triclinic cell with $\text{b = 75.5}\text{A}\text{?}$, β = 93 °, $\text{a =}\text{b}\text{sin}\text{β}$, a = 90 °, $\text{c = n × 668}\text{A}\text{?}$, where n is probably 4 and γ = 90 °. A selection rule observed for prominent reflections is explicable either in terms of a specific orientation of the microfibrils on the lattice, or by a helical distortion of the microfibril axis. The cell parameter β can be varied by changing the ionic envirionment.     

Crystallographic data on a complete kappa-type human Bence-Jones protein.

A complete human κ-type Bence—Jones protein (Fin) has been isolated and crystallized. Immunochemical and physicochemical characterization of protein Fin indicates that it is of the κ-chain subgroup, κII, and that it consists of two non-covalently bound intact monomers having a molecular weight of ~23,000 Crystals of Bence—Jones protein Fin obtained from ammonium sulfate solutions have the orthorhombic space group P2₁2₁2₁ with cell dimensions $\text{a = 132.0}\text{A}\text{?}\text{, b = 93.3}\text{A}\text{?}\text{, and}\text{c = 42.3}\text{A}\text{?}$. The asymmetric unit consists of a dimer of molecular weight ~46,000.     

Wound healing in the imaginal discs of Drosophila. I. Scanning electron microscopy of normal and healing wing discs.

Scanning electron microscopy was used to investigate the morphology of intact imaginal wing discs of third-instar larvae of Drosophila melanogaster. The disc stalk, nerve and tracheal entries and the surface ultrastructure of the columnar cells, the peripodial membrane cells, and the adepithelial cells are described. The behavior of various fragments of the wing disc during culture in vivo was also studied. After injuring a wing disc by cuts with a tungsten needle, during the first day of culture the epithelium curls and the wound surface contracts. Subsequent closure of the wound in $\text{3}\text{4}$ and $\text{1}\text{4}$ sectors, in fragments generated by straight cuts and in central squares, leads to the confrontations of cells from formerly separate positions, as was proposed in connection with the polar coordinate model of French, Bryant, and Bryant [(1976). Pattern regulation in epimorphic fields. Science193, 969–981]. Wound healing comprises three steps: (1) Cell debris is removed; (2) occasional cell processes span the wound; (3) all cells at the wound edge contact cells on the opposite side. After 2–3 days, a continuous epithelium is re-established. The tissue distortion may lead to transient contacts of the columnar epithelium with the peripodial membrane and with itself. The latter can explain the occasional duplications of structures which, according to the fate map, arise from near the wound edge, and which have been previously reported from cultured imaginal disc fragments. The tissue movements appear to be due to the contractile properties of individual cells.     

Structures for the polynucleotide complexes poly(dA) · poly(dT) and poly(dT) · poly(dA) · poly(dT)

X-ray diffraction analyses of fibers of polydeoxyadenylic acid · polydeoxythymidylic acid show that this molecule exists as a 10-fold double-helix with axial rise per nucleotide $\text{h = 3.24}\text{to}\text{3.29}\text{A}\text{?}$. The structure is very similar to B-DNA ($\text{h = 3.37}\text{A}\text{?}$) in having C3-exo furanose rings and base-pairs positioned centrally on the helix axis, but distinctive enough to have two packing modes, neither of which has been observed for B-DNA. Although the triple-stranded poly(dT) · poly(dA) · poly(dT) also has a large value of h(3.26 Å), each of the chains is a 12-fold helix of the A-genus with C3-endo furanose rings and bases displaced several Angstrom units from the helix axis.     

A preliminary crystallographic study of isocitrate dehydrogenase from Azotobacter vinelandii

Large single crystals of isocitrate dehydrogenase from Azotobacter vinelandii have been grown by vapor diffusion from ammonium sulfate and phosphate solutions. The crystals are tetragonal, space group P4₂2₁2 with cell dimensions $\text{a = 122.1}\text{A}\text{?}$, $\text{c = 163.9}\text{a}\text{?}$. There are two molecules of 80,000 molecular weight per asymmetric unit. Native data to 5.5 Å resolution have been collected on a diffractometer. A rotation function using data between 10 Å and 6 Å resolution indicates three possible orientations of the non-crystallographic 2-fold axis relating the two molecules.