The anatomy of the fruit in relation to the propensity of citrus species to split

The anatomy of the fruit has been compared in three prone-to-split mandarin hybrids (Nova, Ellendale and Murcott), several cultivars of clementine mandarin (Fino, Clementina de Nules and Orogrande), and in Owari satsuma mandarin. The fruit of the hybrids is oblate to subglobose and usually presents an open stylar end disrupted by a navel formed by the floral meristem, which is conserved near the apex of the fruit. In the non-prone-to-split clementines as well as in Owari satsuma, the floral axis protrudes inside the style, and the flower meristem is lost through abscission shortly after petal fall. The abaxial side of the carpels fuses with the flower axis forming at the stylar end of the fruit a solid tissue which externally has a small scar at the place of style abscission. Most of the fruits in these cultivars have no navel. In addition, the fruit of clementine is slightly oblate or globose. The relevance of these anatomical characteristics as regards to splitting is supported by the differences between the split and non-split fruits in Nova, the split fruit being more oblate in shape and having a bigger navel than non-split fruit. However, the effect of applied growth regulators on fruit splitting could not be correlated with their effect on the anatomy of the fruit. Additional factors not contemplated in the study also influence fruit splitting

DNA polymerase lambda (Pol λ), a novel eukaryotic DNA polymerase with a potential role in meiosis

A new gene (POLL) encoding a novel DNA polymerase (Pol λ) has been identified at mouse chromosome 19. Murine Pol λ, consisting of 573 amino acid residues, has a 32 % identity to Pol β, involved in nuclear DNA repair in eukaryotic cells. It is interesting that Pol λ contains all the critical residues involved in DNA binding, nucleotide binding and selection, and catalysis of DNA polymerization, that are conserved in Pol β and other DNA polymerases belonging to family X. Murine Pol λ, overproduced in Escherichia coli, displayed intrinsic DNA polymerase activity when assessed by in situ gel analysis. Pol λ also conserves the critical residues of Pol β required for its intrinsic deoxyribose phosphate lyase (dRPase) activity. The first 230 amino acid residues of Pol λ, that have no counterpart in Pol β, contain a BRCT domain, present in a variety of cell-cycle check-point control proteins responsive to DNA damage and proteins involved in DNA repair. Northern blotting, in situ hybridization analysis and immunostaining showed high levels of Pol λ specifically expressed in testis, being developmentally regulated and mainly associated to pachytene spermatocytes. These first evidences, although indirect, suggest a potential role of Pol λ in DNA repair synthesis associated with meiosis.This work has been granted by DGES (PB97-1192) and CAM (08.1/0044/98) to LB; CAM(08.1/0044.2/98) to AB; DGICYT (PB 95-0119), EC PL96-0183 and CAM (07/0022) to JM, and by an institutional grant from Fundación Ramón Areces

DNA polymerase λ, a novel DNA repair enzyme in human cells

DNA polymerase lambda (pol λ) is a novel family X DNA polymerase that has been suggested to play a role in meiotic recombination and DNA repair. The recent demonstration of an intrinsic 5′-deoxyribose-5-phosphate lyase activity in pol λ supports a function of this enzyme in base excision repair. However, the biochemical properties of the polymerization activity of this enzyme are still largely unknown. We have cloned and purified human pol λ to homogeneity in a soluble and active form, and we present here a biochemical description of its polymerization features. In support of a role in DNA repair, pol λ inserts nucleotides in a DNA template-dependent manner and is processive in small gaps containing a 5′-phosphate group. These properties, together with its nucleotide insertion fidelity parameters and lack of proofreading activity, indicate that pol λ is a novel β-like DNA polymerase. However, the high affinity of pol λ for dNTPs (37-fold over pol β) is consistent with its possible involvement in DNA transactions occurring under low cellular levels of dNTPs. This suggests that, despite their similarities, pol β and pol λ have nonredundant in vivo functions.This work was supported by Ministerio de Ciencia y Tecnologı´a Grant BMC2000-1138, Comunidad Auto´noma de Madrid Grant 08.5/0063/2000 (to L. B.) and by an institutional grant from Fundacio´n Ramo´n Areces

Controlled Magnetic Anisotropy in Single Domain Mn-doped Biosynthesized Nanoparticles

Magnetotactic bacteria Magnetospirillum gryphiswaldense synthesize cubo-octahedral shaped magnetite nanoparticles, called magnetosomes, with a mean diameter of 40 nm. The high quality of the biosynthesized nanoparticles makes them suitable for numerous applications in fields like cancer therapy, among others. The magnetic properties of magnetite magnetosomes can be tailored by doping them with transition metal elements, increasing their potential applications. In this work, we address the effect of Mn doping on the main properties of magnetosomes by the combination of structural and magnetic characterization techniques. Energy-dispersive X-ray spectroscopy, X-ray absorption nearedge structure, and X-ray magnetic circular dichroism results reveal a Mn dopant percentage of utmost 2.3%, where Mn cations are incorporated as a combination of Mn2+ and Mn3+, preferably occupying tetrahedral and octahedral sites, respectively. Fe substitution by Mn notably alters the magnetic behavior of the doped magnetosomes. Theoretical modeling of the experimental hysteresis loops taken between 5 and 300 K with a modified Stoner-Wohlfarth approach highlights the different anisotropy contributions of the doped magnetosomes as a function of temperature. In comparison with the undoped magnetosomes, Mn incorporation alters the magnetocrystalline anisotropy introducing a negative and larger cubic anisotropy down to the Verwey transition, which appears shifted to lower temperature values as a consequence of Mn doping. On the other hand, Mn-doped magnetosomes show a decrease in the uniaxial anisotropy in the whole temperature range, most likely associated with a morphological modification of the Mn-doped magnetosomes.The Spanish and Basque Governments are acknowledged for funding under project numbers MAT2017- 83631-C3-R and IT-1245-19, respectively

Identification of an intrinsic 5′-deoxyribose-5-phosphate lyase activity in human DNA polymerase λ: A possible role in base excision repair

Base excision repair (BER) is a major repair pathway in eukaryotic cells responsible for repair of lesions that give rise to abasic (AP) sites in DNA. Pivotal to this process is the 5′-deoxyribose-5-phosphate lyase (dRP lyase) activity of DNA polymerase β (Pol β). DNA polymerase λ (Pol λ) is a recently identified eukaryotic DNA polymerase that is homologous to Pol β. We show here that human Pol λ exhibits dRP lyase, but not AP lyase, activityin vitro and that this activity is consistent with a β-elimination mechanism. Accordingly, a single amino acid substitution (K310A) eliminated more than 90% of the wild-type dRP lyase activity, thus suggesting that Lys310 of Pol λ is the main nucleophile involved in the reaction. The dRP lyase activity of Pol λ, in coordination with its polymerization activity, efficiently repaired uracil-containing DNA in an in vitroreconstituted BER reaction. These results suggest that Pol λ may participate in “single-nucleotide” base excision repair in mammalian cells.This work was supported by Direccio´n General de Ensenanza Superior Grant PB97-1192, Comunidad Autónoma de Madrid Grants 08.1/0044/98 and 08.5/0063/2000 (to L. B.), and by an institutional grant from Fundación Ramón Areces

Diastereoselective Synthesis of Chiral Octahedral Iridium(III) Phosphano–Oxazoline Complexes

Reaction of the dimer [Ir­(μ-Cl)­(η²-coe)₂]₂ (coe = cyclooctene) with chiral phosphano–oxazoline ligands (PN*) renders neutral mononuclear iridium­(I) complexes of the formula [IrCl­(η²-coe)­(PN*)] (<b>1</b>, <b>2</b>), which in turn are oxidized to the corresponding iridium­(III) hydride species [IrCl₂H­(η²-coe)­(PN*)] (<b>3</b>, <b>4</b>) by treatment with aqueous HCl. The latter react with diphosphanes (PP) in the presence of NaSbF₆ to afford cationic complexes of stoichiometry [IrClH­(PN*)­(PP)]­[SbF₆] (<b>5</b>–<b>16</b>). The fluorophenyldiphosphane-containing compounds [IrClH­(PN*)­(dfppe)]­[SbF₆] (<b>15</b>, <b>16</b>) evolve to the corresponding Ir­(I) species [Ir­(PN*)­(dfppe)]­[SbF₆] (<b>17</b>, <b>18</b>) by HCl loss. The new compounds have been fully characterized by analytical and spectroscopic means, including the molecular structure determination of [IrCl₂H­(η²-coe)­(PNInd)] (<b>3</b>), [IrClH­(PNInd)­(dppen)]­[SbF₆] (<b>6a</b>,<b>b</b>), [IrClH­(PNInd)­(dppp)]­[SbF₆] (<b>7a</b>), [IrClH­(PN<i>i</i>Pr)­(dppp)]­[SbF₆] (<b>13a</b>), [IrClH­(PNInd)­(dfppe)]­[SbF₆] (<b>15</b>), [Ir­(PNInd)­(dfppe)]­[SbF₆] (<b>17</b>), and [Ir­(PN<i>i</i>Pr)­(dfppe)]­[SbF₆] (<b>18</b>) by X-ray diffractometric methods

Chiral Octahedral Phosphano–Oxazoline Iridium(III) Complexes as Catalysts in Asymmetric Cycloaddition Reactions

The synthesis and characterization of cationic iridium­(III) aqua complexes of the formula [IrH­(H₂O)­(PN*)­(PP)]­[SbF₆]₂ (PN* = chiral phosphano–oxazoline ligand; PP = diphosphane) as well as that of the OPOF₂-containing complex [IrH­(OPOF₂)­(PN<i>i</i>Pr)­(dppp)]­[SbF₆] (<b>10</b>) are reported. The X-ray molecular structures of [IrH­(H₂O)­(PNInd)­(dppe)]­[SbF₆]₂ (<b>1</b>), [IrH­(H₂O)­(PNInd)­(dppen)]­[SbF₆]₂ (<b>2</b>), and <b>10a</b> have been determined. Dichloromethane solutions of these aqua complexes efficiently catalyze the enantioselective 1,3-dipolar cycloaddition of the nitrone <i>N</i>-benzylidenephenylamine <i>N</i>-oxide to methacrolein and Diels–Alder reactions between cyclopentadiene and <i><i>trans</i></i>-β-nitrostyrenes. In the first case, the catalytic reaction occurs with excellent <i>endo</i> selectivity and ee up to 85%; the Diels–Alder reaction occurs rapidly at room temperature with good <i>endo</i>:<i>exo</i> selectivity and ee up to 90%. The dipolar cycloaddition intermediates [IrH­(methacrolein)­(PNInd)­(PP)]­[SbF₆]₂ (PP = (<i>S,S</i>)-chiraphos (<b>11</b>), (<i>R</i>)-prophos (<b>12</b>)) have been characterized, and the molecular structure of <b>11</b> has been determined by an X-ray structural analysis

Metal–Nitroalkene and <i>aci</i>-Nitro Intermediates in Catalytic Enantioselective Friedel–Crafts Reactions of Indoles with <i>trans</i>-β-Nitrostyrenes

The half-sandwich aqua complex (<i>S</i>_Rh,<i>R</i>_C)-[(η⁵-C₅Me₅)­Rh­{(<i>R</i>)-Prophos}­(H₂O)]­[SbF₆]₂ (Prophos = propane-1,2-diylbis­(diphenylphosphane)) efficiently catalyzes the asymmetric reaction between <i>N</i>-methyl-2-methylindole and <i>trans</i>-β-nitrostyrenes (up to 94% ee). The metal–nitroalkene complex involved has been characterized by X-ray crystallography, and the <i>aci</i>-nitro intermediate complex has been spectroscopically detected. A plausible catalytic cycle is proposed