The TS ribozyme (originally called "twister sister") is a catalytic RNA. We present a crystal structure of the ribozyme in a pre-reactive conformation. Two co-axial helical stacks are organized by a three-way junction and two tertiary contacts. Five divalent metal ions are directly coordinated to RNA ligands, making important contributions to the RNA architecture. The scissile phosphate lies in...

H-N-H is a motif found in the nuclease domain of a subfamily of bacteria toxins, including colicin E7, that are capable of cleaving DNA nonspecifically. This H-N-H motif has also been identified in a subfamily of homing endonucleases, which cleave DNA site specifically. To better understand the role of metal ions in the H-N-H motif during DNA hydrolysis, we crystallized the nuclease domain of c...

Citrate uptake in Bacillus subtilis is stimulated by a wide range of divalent metal ions. The metal ions were separated into two groups based on the expression pattern of the uptake system. The two groups correlated with the metal ion specificity of two homologous B. subtilis secondary citrate transporters, CitM and CitH, upon expression in Escherichia coli. CitM transported citrate in complex ...

The structure- and strand-specific phosphodiesterase flap endonuclease-1 (FEN1), the prototypical 5'-nuclease, catalyzes the essential removal of 5'-single-stranded flaps during replication and repair. FEN1 achieves this by selectively catalyzing hydrolysis one nucleotide into the duplex region of substrates, always targeting the 5'-strand. This specificity is proposed to arise by unpairing the...

Transition metals are essential for many metabolic processes, and their homeostasis is crucial for life. Metal-ion transporters play a major role in maintaining the correct concentrations of the various metal ions in living cells. Little is known about the transport mechanism of metal ions by eukaryotic cells. Some insight has been gained from studies of the mammalian transporter DCT1 and the y...

The aim of this study was to investigate the effect of divalent metal ions (Ca, Mg(2+) , and Zn(2+) ) on the stability of oxytocin in aspartate buffer (pH 4.5) and to determine their interaction with the peptide in aqueous solution. Reversed-phase high-performance liquid chromatography and high-performance size-exclusion chromatography measurements indicated that after 4 weeks of storage at 55°...

The propert ies of rumen urease were studied. In the absence of high concentrations of dithiothreitol enzyme activity was rapidly lost; in its presence, the enzyme could be solubilized and purified in high yield. Maximum activity was observed between pH 7 and 8.5. The Km for urea with partially purified enzyme was .004 M with Vmax of 300 to 400 #moles/mg/hr. No divalent metal ion requirement or...

The ionophoretic antibiotics, monensin and lasalocid, bind numerous mono- and divalent cations, primarily in dimeric complexes that facilitate the passage of metal ions through hydrophobic lipid membranes. Ionophores vary in their affinity for metal ions. Similarly, transport rates of the resulting complexes depend in part upon the affinity constant of the drug ion-binding interaction, and in p...