RESUMO
The ditopic ligand PyPzOAPz (N-[(Z)-amino(pyrazin-2-yl)methylidene]-5-methyl-1-(pyridin-2-yl)-1H-pyrazole-3-carbohydrazonic acid) was synthesized by in situ condensation of methyl imino pyrazine-2-carboxylate with 5-methyl-1-(2-pyridyl) pyrazole-3-carbohydrazide. In this work we have also used two of our earlier ligands PzCAP (5-methyl-N-[(1E)-1-(pyridin-2-yl)ethylidene]-1H-pyrazole-3-carbohydrazonic acid) (Dalton Trans., 2009, 8215) and PzOAP (N-[(Z)-amino(pyridin-2-yl)methylidene]-5-methyl-1H-pyrazole-3-carbohydrazonic acid) (Dalton Trans., 2007, 1229). These ligands PzCAP, PzOAP and PyPzOAPz were made to react with Mn(ClO(4))(2)·6H(2)O to produce three pentanuclear Mn(II) clusters [Mn(5)(PzCAP)(6)](ClO(4))(4) (1), [Mn(5)(PzOAP)(6)](ClO(4))(4) (2) and [Mn(5)(PyPzOAPz)(6)](ClO(4))(4) (3). These complexes have been characterized by X-ray structural analyses and variable temperature magnetic susceptibility measurements. All complexes have a pentanuclear core with trigonal bipyramidal arrangement of Mn(II) atoms, where, the axial metal centers have a N(3)O(3) chromophore and the equatorial centers have N(4)O(2) with an octahedral arrangement. These Mn(5)(II) clusters 1, 2 and 3 show the presence of antiferromagnetic coupling within the pentanuclear manganese(II) core (J = -2.95, -3.19 and -3.00 cm(-1) respectively). Density functional theory calculations and continuous shape measurement (CShM) studies have been performed on these complexes to provide a qualitative theoretical interpretation of the antiferromagnetic behaviour shown by them. The pentanuclear Mn(II) cluster (1) on reaction with Cu(NO(3))(2)·6H(2)O in 1:1 mole proportion in CH(3)OH:H(2)O (60 : 40) forms a homoleptic [2 × 2] tetranuclear Cu(4)(II) grid [Cu(4)(PzCAP)(4)(NO(3))(2)](NO(3))(2)·8H(2)O (4). The same Cu(4)(II) grid is also obtained from a direct reaction between the ditopic ligand PzCAP with Cu(NO(3))(2)·6H(2)O in 1:1 mole proportion. This conversion of a cluster to a grid is a novel observation.
Assuntos
Complexos de Coordenação/síntese química , Hidrazinas/química , Magnetismo , Manganês/química , Modelos Moleculares , Pirazóis/química , Complexos de Coordenação/química , Cristalografia por Raios X , Hidrazinas/síntese química , Ligantes , Imãs , Conformação Molecular , Pirazóis/síntese químicaRESUMO
The RusA protein of Escherichia coli is an endonuclease that can resolve Holliday intermediates and correct the defects in genetic recombination and DNA repair associated with inactivation of RuvAB or RuvC. The structure of the rusA gene, its organisation in the genome, and its interaction with the Ruv and RecG proteins have been investigated. Recombinant plasmids carrying rusA were identified by their ability to make ruv mutants resistant to UV light. The gene was located to an open reading frame encoding a polypeptide of 120 amino acids. It forms the fifth gene in an operon containing a chain of short, interlinked open reading frames. A similar arrangement was found in the genome of the lambdoid bacteriophage, 82. The two rusA genes show 95% sequence identity. The E. coli operon forms part of the defective lambdoid prophage, DLP12, and is probably derived from a phage related to 82 and PA-2. rusA appears to be very poorly expressed in E. coli, but can be activated by insertion of IS2 or IS10 upstream of the coding sequence to promote transcription. These insertions arise spontaneously in ruv strains as suppressors of the mutant phenotype. Deletion of rusA from the chromosome of either wild-type or ruv mutant strains has no obvious effect on recombination or sensitivity to UV light. Multicopy plasmids expressing RusA alone make ruvA, ruvB, and ruvC mutants resistant to UV light. Suppression depends critically on RecG.
Assuntos
Bacteriófagos/genética , DNA Helicases , DNA Nucleotidiltransferases/genética , Proteínas de Escherichia coli , Escherichia coli/genética , Genes Bacterianos , Genes Virais , Sequência de Aminoácidos , Proteínas de Bactérias/genética , Proteínas de Bactérias/metabolismo , Bacteriófagos/enzimologia , Sequência de Bases , DNA Nucleotidiltransferases/metabolismo , Proteínas de Ligação a DNA/genética , Proteínas de Ligação a DNA/metabolismo , Endodesoxirribonucleases/genética , Endodesoxirribonucleases/metabolismo , Escherichia coli/enzimologia , Dados de Sequência Molecular , Recombinação Genética , Alinhamento de Sequência , Análise de Sequência , TransposasesRESUMO
The ruvA, ruvB, and ruvC genes of Escherichia coli provide activities that catalyze branch migration and resolution of Holliday junction intermediates in recombination. Mutation of any one of these genes interferes with recombination and reduces the ability of the cell to repair damage to DNA. A suppressor of ruv mutations was identified on the basis of its ability to restore resistance to mitomycin and UV light and to allow normal levels of recombination in a recBC sbcBC strain carrying a Tn10 insertion in ruvA. The mutation responsible was located at 12.5 min on the genetic map and defines a new locus which has been designated rus. The rus suppressor works just as well in recBC sbcA and rec+ sbc+ backgrounds and is not allele specific. Mutations in ruvB and ruvC are suppressed to an intermediate level, except when ruvA is also inactive, in which case suppression is complete. In all cases, suppression depends on RecG protein, a DNA-dependent ATPase that catalyzes branch migration of Holliday junctions. The rus mutation activates an additional factor that probably works with RecG to process Holliday junction intermediates independently of the RuvAB and RuvC proteins. The possibility that this additional factor is a junction-specific resolvase is discussed.
