236 ERNST FREESE 



enough alkyl groups icniain attached uj) to the time at which tlie DNA 

 attempts to duplicate, tlie duplication might be inhibited. The attached 

 alkyl group might conceivably (but not likely) intei'fere with the DNA 

 (hiplication in such a way that some non-com])lementary base would be 



iiicoi-porated into the new strand. 



Al Al 



I I 



1. S— Ph-S-Ph-S-Ph— S-Ph-S— Ph 



I I I I I 



B B B B B 



Al Al 



' II > 



S — Ph-S-Ph— S— Ph-S Ph-S— Ph 



I I I I " I 



B B B B B 



Al Al 



I I 



S— Ph— S— Ph— S— Ph— S-Ph— S— Ph 



I I I I I 



B B B B B 



I I 



Al Al 



Al Al 



I I 



S— Ph— S — Ph— S— Ph— S— Ph-S— Ph 

 I III 



B B B B B 



5. S-Ph-S Ph— S— Ph— S-Ph— S— Ph 



I "ill 



B B B B B 



I I 



Al Al 



Fig. 13. Various reactions of alkylating agonts with DXA (see text for ex- 

 planation). 



2. The phosphate triester can occasionally also hydrolyze between 

 the sugar and the phosphate and thus the DNA backbone gets broken. 

 The relative frequencies with which the alkyl group becomes removed 

 or the chain is broken are not known. Chain breakage might induce 

 larger alterations or be lethal, but probably does not induce point 

 mutations. 



3. Some of the bases are alkylated (see Fig. 13). Treatment of DNA 



