Coding properties of 7-methylguanine

The abnormal base, 7-methylguanine, has been introduced into copolymers of uridylic and guanylic acids by methylation under controlled conditions. The resulting methylated copolymers have a markedly decreased template activity for polypeptide synthesis in vitro due to steric effects of the 7-methyl groups. Contrary to expectation, these polymers do not permit incorporation of amino acids whose codons contain the bases uracil and adenine.