Synthesis and properties of poly(O6-methylguanylic acid) and poly(O6-ethylguanylic acid)

Abstract

The nucleotide analogs, O6-methyl- and O6-ethylGDP, were synthesized and polymerized to high molecular weight homopolymers with polynucleotide phosphorylase. The UV spectra of these polymers show marked hypochromicity, which suggests that they possess considerable secondary structures. Graphs of optical density vs. temperature in 0.15 M NaCl indicate that cooperative melting occurs for both polymers, and the secondary structure of poly(O6-methylGMP) is somewhat more stable than that of poly(O6-ethylGMP). Mixing experiments show that these analog polymers no longer form helical structures with poly(C), nor do they form helices with poly(U). Environmental mutagens and carcinogens which react at the O6 position of guanine not only disrupt normal base pairing relationships, but may also affect the secondary structure of nucleic acids.