Mutagenic Alkylating Agents 315 



agents as a result of the instability of the tricsters produced. 

 Although in the majority of the hydrolyses the alkylating 

 agent is split off again, occasionally the sugar ester is hydro- 

 lysed and this brings with it an interruption of the chain. 

 Table VI illustrates the change (on standing at 37° C) in 



Table VI 



Production of "single" and "double" breaks in DNA 



t Even this small degree of esterification was sufficient to bring about appreciable internal 

 crosslinking. 



molecular weight due to hydrolysis of DNA treated with 

 alkylating agent. The existence of hidden breaks is very 

 clearly revealed after extensive treatment with the mono- 

 functional epoxide, propylene oxide. The molecular weight 

 of the double molecule is unchanged while after splitting it is 

 reduced to approximately one-fifteenth. With the bifunc- 

 tional reagents the number of hidden breaks cannot be deter- 

 mined since the two chains are covalently crosslinked and this 

 prevents the splitting into two strands by the urea except 

 when there are breaks in the main chain to compensate for 



