DNA helicase I, the traI gene product of the Escherichia coli F factor, was shown to be associated with endonuclease activity specific for the transfer origin of the F plasmid, oriT. In the presence of Mg2+, the purified enzyme forms a complex, stable in the presence of sodium dodecylsulfate (SDS) with a negatively superhelical chimeric plasmid containing oriT. The enzyme nicks and, after this, apparently binds to the 5′ nick terminus when this complex is heated in the presence of SDS and/or EDTA or treated with proteinase K. Dideoxy sequencing locates the nick site in the F DNA strand transferred during bacterial conjugation after nucleotide 138 clockwise of the mid‐point of the BglII site at 66.7 kb of the F genetic map. A sequencing stop after nucleotide 137 of this strand (where oriT‐nicking seems to occur in vivo) is possibly an artefact caused by helicase I protein attached to the 5′ terminal nucleotide. Deletion in the amino‐terminal part of the traI polypeptide abolishes the oriT‐nicking activity while leaving the strand‐separating activity intact. These results confirm the prediction from genetic studies that helicase I is bifunctional with site‐specific endonuclease and strand‐separating activities.

Herein, we report the synthesis of two phenylaza-[18]crown-6 lariat ethers with a coumarin fluorophore (1 and 2) and we reveal that compound 1 is an excellent probe for K(+) ions under simulated physiological conditions. The presence of a 2-methoxyethoxy lariat group at the ortho position of the anilino moiety is crucial to the substantially increased stability of compounds 1 and 2 over their lariat-free phenylaza-[18]crown-6 ether analogues. Probe 1 shows a high K(+)/Na(+) selectivity and a 2.5-fold fluorescence enhancement was observed in the presence of 100 mM K(+) ions. A fluorescent membrane sensor, which was prepared by incorporating probe 1 into a hydrogel, showed a fully reversible response, a response time of 150 s, and a signal change of 7.8% per 1 mM K(+) within the range 1-10 mM K(+). The membrane was easily fabricated (only a single sensing layer on a solid polyester support), yet no leaching was observed. Moreover, compound 1 rapidly permeated into cells, was cytocompatible, and was suitable for the fluorescent imaging of K(+) ions on both the extracellular and intracellular levels.

Enge Kanäle mit polaren Wänden bestimmen Struktur und Funktion eines Metall‐organischen Gerüsts aus Zinkionen und einem Imidazolat‐Amid‐Imidat‐Liganden (siehe Struktur: Zn orange, N blau, O rot, C dunkelgrau, H hellgrau), das über eine hohe Aufnahmekapazität für H2 und CO2 verfügt. Der starre und stabile Chelatligand entsteht in situ durch partielle Hydrolyse eines Dicyanimidazols.

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The new π-conjugated 1,2,3-triazol-1,4-diyl fluoroionophore 1 generated via Cu(I) catalyzed [3 + 2] cycloaddition shows high fluorescence enhancement factors (FEF) in the presence of Na(+) (FEF=58) and K(+) (FEF=27) in MeCN and high selectivity towards K(+) under simulated physiological conditions (160 mM K(+) or Na(+), respectively) with a FEF of 2.5 for K(+).