DNA/RNA duplexes containing metal-ionmediated base pairs (metallo-base pairs) have potential applications in developing nucleic acid-based nanodevices and genetic code expansion. Many metallo-base pairs are formed within duplexes stabilized by Watson-Crick base pairs. Recently, the crystal structure of an Ag I -DNA nanowire with an uninterrupted one-dimensional silver array was determined. Here, we present a new DNA helical wire, the "Ag I -DNA rod", containing an uninterrupted array of 11 Ag I ions. The Ag I -DNA rod consisted of only C-Ag I -C, G-Ag I -G, G-Ag I -5bromouracil ( Br U), and Br U-Ag I -Br U metallo base pairs, with no Watson-Crick pairs. The Ag I -DNA rods were connected by non-canonical G-G pairs in crystals. Notably, data from our absorbance, circular dichroism, nuclear magnetic resonance, and mass spectrometry analyses suggested that the Ag I -DNA rods formed in solution, as well as within crystals.DNA can be used as a basic template to generate functional molecules, precise molecular architectures, and nanoscale devices. [1] Recently, duplexes containing metal ion-mediated base pairs (metallo-base pairs) have been characterized. [2] Investigations of the metal-mediated pairing of natural and artificial bases have considerably expanded the design space for developing functional DNA molecules. [2] For example, metallo-base pair-forming oligonucleotides have been applied to develop DNA molecular devices such as ion-sensors, [3] electric transport nano-wires, [4] and DNA magnets. [5] Short oligonucleotides and metal ions can be mixed together to form metallo-base pairs, generating relatively small double-helical and triple-helical structures containing both metallo-base pairs and Watson-Crick base pairs. [2] Recently, the structures of short duplexes containing metal-lo-base pairs have been determined, [2] including the crystal structures of metallo-base pair duplexes composed of artificial and natural bases. [6] Heteronuclear multidimensional nuclear magnetic resonance (NMR) has also been applied to resolve the structures of metallo-base pairs in solution. [7] Recently, two types of metal-DNA nanowire have been generated in crystal form. [6f,g] Crystals containing long Ag I -DNA nanowires with uninterrupted one-dimensional silver arrays were generated by mixing short oligonucleotides with Ag I ions. [6f] In the presence of Ag I ions, the short oligonucleotides formed double-helical structures comprising only metallo-base pairs and sticky 5'-ends. The short double-helical structures were then linked together to form long Ag I -DNA nanowires, in which the Ag I ions were precisely aligned to form one-dimensional silver arrays. The second type of metal-DNA wire structure comprised Hg IImediated T : T and T : G base pairs and water-mediated C : C base pairs; this structure was observed in crystals produced by mixing the short oligonucleotide 5'-d(TTTGC)-3' with Hg II ions. [6g] Neither the Ag I -DNA nor Hg II -DNA wires contained Watson-Crick base pairs. These metallo-DNA wire structures were pre...

DNA/RNA duplexes containing metal-ionmediated base pairs (metallo-base pairs) have potential applications in developing nucleic acid-based nanodevices and genetic code expansion. Many metallo-base pairs are formed within duplexes stabilized by Watson-Crick base pairs. Recently, the crystal structure of an Ag I -DNA nanowire with an uninterrupted one-dimensional silver array was determined. Here, we present a new DNA helical wire, the "Ag I -DNA rod", containing an uninterrupted array of 11 Ag I ions. The Ag I -DNA rod consisted of only C-Ag I -C, G-Ag I -G, G-Ag I -5bromouracil ( Br U), and Br U-Ag I -Br U metallo base pairs, with no Watson-Crick pairs. The Ag I -DNA rods were connected by non-canonical G-G pairs in crystals. Notably, data from our absorbance, circular dichroism, nuclear magnetic resonance, and mass spectrometry analyses suggested that the Ag I -DNA rods formed in solution, as well as within crystals.DNA can be used as a basic template to generate functional molecules, precise molecular architectures, and nanoscale devices. [1] Recently, duplexes containing metal ion-mediated base pairs (metallo-base pairs) have been characterized. [2] Investigations of the metal-mediated pairing of natural and artificial bases have considerably expanded the design space for developing functional DNA molecules. [2] For example, metallo-base pair-forming oligonucleotides have been applied to develop DNA molecular devices such as ion-sensors, [3] electric transport nano-wires, [4] and DNA magnets. [5] Short oligonucleotides and metal ions can be mixed together to form metallo-base pairs, generating relatively small double-helical and triple-helical structures containing both metallo-base pairs and Watson-Crick base pairs. [2] Recently, the structures of short duplexes containing metal-lo-base pairs have been determined, [2] including the crystal structures of metallo-base pair duplexes composed of artificial and natural bases. [6] Heteronuclear multidimensional nuclear magnetic resonance (NMR) has also been applied to resolve the structures of metallo-base pairs in solution. [7] Recently, two types of metal-DNA nanowire have been generated in crystal form. [6f,g] Crystals containing long Ag I -DNA nanowires with uninterrupted one-dimensional silver arrays were generated by mixing short oligonucleotides with Ag I ions. [6f] In the presence of Ag I ions, the short oligonucleotides formed double-helical structures comprising only metallo-base pairs and sticky 5'-ends. The short double-helical structures were then linked together to form long Ag I -DNA nanowires, in which the Ag I ions were precisely aligned to form one-dimensional silver arrays. The second type of metal-DNA wire structure comprised Hg IImediated T : T and T : G base pairs and water-mediated C : C base pairs; this structure was observed in crystals produced by mixing the short oligonucleotide 5'-d(TTTGC)-3' with Hg II ions. [6g] Neither the Ag I -DNA nor Hg II -DNA wires contained Watson-Crick base pairs. These metallo-DNA wire structures were pre...