ABSTRACT
Alkylation of DNA is an important step in the biological efects of alkylating agents. In an attempt to determine the effect of alkylation at Ν 1 and Ν 3-positions in adenine, diploid yeast auxotrophic to adenine was cultured in synthetic medium in which adenine was replaced by Ν 1 or Ν 3-methyladenines. The expectation was that, the cells will incorporate methyladenines to the DNA newly synthesised by the salvage pathway and thus facilitate the expression of their biological effects, if any. The biological end points monitored were cell killing, gene conversion and reverse mutation. Contrary to expectation, no growth occurred in the cultures even after 48 h of incubation. The cells retained viability, but were only arrested in growth. When subcultured in the presence of sub-optimum levels of both adenine and Ν 1- methyladenine complete growth occurred. However, no enhancement in the induction of gene conversion or back mutation was observed in these cultures. Experiments with tritium labelled Ν 1-methyladenine showed that it is taken up by the cells. Hence, it is speculated that the ineffectiveness of methyladenines is due to their not being utilised as substrates in the synthesis of DNA by the salvage pathway. This is important for the assessment of the biological effects of DNA precursor pool alkylation.