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Poly(8-methyladenylic acid): a single-stranded regular structure with alternating syn-anti conformations.

Authors
  • Limm, W
  • Uesugi, S
  • Ikehara, M
  • Miles, H T
Type
Published Article
Journal
Biochemistry
Publication Date
Aug 30, 1983
Volume
22
Issue
18
Pages
4217–4222
Identifiers
PMID: 6626503
Source
Medline
License
Unknown

Abstract

Poly(8-methyladenylic acid) has been prepared by chemical synthesis of 8-methyladenosine 5'-diphosphate and enzymatic polymerization with polynucleotide phosphorylase. The polymer exhibits a large hypochromism and cooperative melting in neutral solution. The transition temperature is independent of salt concentration at moderate ionic strength and decreases slightly at high salt. The adenine ring vibration at 1626 cm-1 is independent of temperature. A high-resolution nuclear magnetic resonance spectrum is observed near the bottom of the melting range. The chemical shift of the H2 proton exhibits a large upfield shift in the ordered form, and the temperature profile of H2 is cooperative and congruent with the UV melting curve. The CH3 proton signal, in striking contrast to H2, is independent of temperature. These results support a regular, single-stranded helix in the ordered form, in contrast to both poly(adenylic acid) and poly(8-bromoadenylic acid). We suggest that the contrasting temperature dependence of the H2 and CH3 proton signals can be accounted for by regularly alternating syn and anti conformations of the 8-methyladenylic acid residues.

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