DNA homoduplexes containing no pyrimidine nucleotide

We show using polyacrylamide gel electrophoresis that guanine+adenine repeat strands of DNA associate into homoduplexes at neutral pH and moderate ionic strength. The homoduplexes melt in a cooperative way like the Watson-Crick duplex, although they contain no Watson-Crick base pair. Guanine is absolutely needed for the homoduplex formation and the homoduplex stability increases with the guanine content of the repeat. The present results have implications for the nature of the first replicators, as well as regarding forces stabilizing the duplexes of DNA.