The occurrence of 6-methylaminopurine in deoxyribonucleic acids.

While investigating the effects of structural analogues of thymine on the thymine-requiring strain of E&cherichia coli 15 T we noticed the presence in the bacterial deoxyribonucleic acid of a new base which we have identified as 6-methylaminopurine. Although 6-methylaminopurine is usually present in small amounts (2% of the adenine) in the deoxyribonucleic acid of E. coli 15 Tits relative proportion increases considerably during growth of the bacteria in thymine-deficient conditions, obtained either by maintaining the thymine concentration in the medium at a low level, or by the addition of thymine antagonists such as 5-aminouracil or 2-thiothymine. Examination of a number of deoxyribonucleic acids has shown that 6-methylaminopurine also occurs in small proportions as a constituent of deoxyribonucleic acid from several bacteria and bacterial viruses. This paper describes the identification of 6-methylaminopurine, its deoxyribonucleoside and deoxyribonucleotide from deoxyribonucleic acid of E. coli 15 T, and the occurrence of the base in other deoxyribonucleic acids. Brief accounts of this work have appeared previously (Dunn & Smith, 1955a, b).