title: Poly(7-deazaguanylic acid), the homopolynucleotide of the parent nucleoside of queuosine.
abstract: Poly(7-deazaguanylic acid) was enzymatically synthesized by the polymerization of 7-deazaguanosine 5'-diphosphate with polynucleotide phosphorylase from Micrococcus luteus in high yield. The homopolymer showed a similar thermal and total hypochromicity to poly(G) at the long wavelength absorption maximum. No sigmoid melting profile was observed for poly(c7G) as is found for poly(G), implying a single-stranded structure in aqueous solution. From the circular dichroism spectra it can be concluded that the 7-deazapurine nucleotide is much more flexible than the purine nucleotide. In analogy to poly(G), the homopolymer poly(c7G) forms a 1:1 complex with poly(C) under neutral conditions, melting at a similar temperature to the poly(G) complex. However, at pH 2.5, where a poly(G) X 2poly(C) complex is observed, poly(c7G) still binds only one poly(C) strand. This is due to the lack of N-7 in poly(c7G), not allowing Hoogsteen base pair formation, which occurs with poly(G). RNase T1 cleaves poly(c7G), indicating that N-7 of guanosine is not a requirement for nucleotide binding to the enzyme, as has been suggested. Because of the single-stranded structure of poly(c7G), the polynucleotide chain is rapidly hydrolyzed by the single-strand-specific nuclease S1, whereas multistranded poly(G) is completely resistant.
mesh_terms: D001482:Base Composition; D004720:Endonucleases / Q000378:metabolism; D004926:Escherichia coli / Q000201:enzymology; D006358:Hot Temperature; D006868:Hydrolysis; D008837:Micrococcus / Q000201:enzymology*; D011066:Poly C; D011068:Poly G / Q000138:chemical synthesis*; D011117:Polyribonucleotide Nucleotidyltransferase / Q000378:metabolism*; D011131:Polyribonucleotides / Q000138:chemical synthesis*; D006163:Ribonuclease T1 / Q000378:metabolism; D015719:Single-Strand Specific DNA and RNA Endonucleases; D013056:Spectrophotometry, Ultraviolet
chemical_list: D011131:Polyribonucleotides; D011068:Poly G; D011066:Poly C; C036039:poly(7-deazaguanylic acid); D011117:Polyribonucleotide Nucleotidyltransferase; D004720:Endonucleases; D006163:Ribonuclease T1; D015719:Single-Strand Specific DNA and RNA Endonucleases