The alkaline hydrolysis of phosphotriesters in alkylated mammalian DNA.

Isolated DNA was alkylated with N-[14C]methyl-N-nitrosourea or N-[14C]ethyl-N-nitrosourea. Sedimentation analysis of the alkylated DNA before and after alkaline hydrolysis was used to determine the number of single-strand breaks introduced by hydrolysis of the triesters. Vacuum distillation from alkylated DNA solutions before and after alkaline hydrolysis was used to determine the numbers of triesters hydrolysing to the alcohol.

The stability of methylated purines and of methylphosphotriesters in the DNA of V79 cells after treatment with N-methyl-N-nitrosourea.

V79-379A cells growing in suspension culture were treated with N-methyl-N-nitrosourea at concentrations of 0.6 and 1.2 mM.

Repair processes and the response of dividing and non-dividing cells to methyl methanesulphonate and dimethyl sulphate.

A method for producing a viable non-dividing population of Chinese hamster V79 cells in suspension is described and the characteristics of the population outlined. The stationary population is more sensitive to methylating agents than a similar but exponentially growing population, the increased sensitivity arising from the loss of the shoulder from the survival curve. The extent of reaction of the agent with cellular macromolecules is similar in both cases.

Biomethylation of deoxyribonucleic acid in cultured human tumour cells (HeLa). Methylated bases other than 5-methylcytosine not detected.

1. Incorporation of methyl groups from [methyl-(14)C]methionine into DNA of dividing HeLa cells was investigated, essentially by the procedures of Culp, et al. (1970).