USE OF FLUORESCENTLY TAGGED DNA AND AN AUTOMATED DNA SEQUENCER FOR THE COMPARISON OF THE SEQUENCE SELECTIVITY OF SN1 AND SN2 ALKYLATING-AGENTS

This paper describes the application of the novel non-radioactive technique for studying the sequence selectivity of selected alkylating agents. N-Nitroso-N-methylurea (MNU) and N-methyl-N-nitro-nitrosoguanidine (MNNG) were chosen from the S(N)1 group of alkylating agents. Dimethyl sulphate (DMS) was used to represent alkylation profile produced by the S(N)2 compounds. Results of S(N)1 compounds indicated that in a run (G)3 the latter two Gs are more susceptible to alkylation than the most 5' G. Moreover, in a GG sequence the 3' G seems to be more alkylated. This effect is more evident when the GG site was preceded by a 5' pyrimidine. These findings suggest that a regio-selective mechanism, rather than the formation of diazonium ions, accounts for DNA alkylation by SN1 compounds. On the other hand, DMS showed preferential alkylation of the 5' end in a (G)3 run. However, at GG sequences no clear preferred site of alkylation could be distinguished. Lack of specificity of S(N)2 compound would seem to suggest that other factors as well as the primary DNA structure may play a role in determining the extent of alkylation at a certain site.