DNA strand breaks induced by gamma irradiation and alkaline treatment: a computer program for the analysis of the influence of the sequence.

Deoxyoligonucleotides 32P-labelled at one end have been used to probe the DNA chain breakage induced by external gamma-irradiation and alkali treatment. The fragments were separated according to their chain lengths by polyacrylamide gel electrophoresis and their radioactivity counted. Quantitative analysis of the distribution pattern of the intensity fragments was performed by computer. In this article the principles of the calculation program are given. The basic units corresponding to adenine, thymine, cytosine and guanine exhibited different radiosensitivities. It was possible to estimate the mean chain rupture per nucleotide and per Gray for G, T, C and A. These coefficients were derived from experimental values by iteration. Thus, it is possible to simulate very accurately the oligonucleotide fragment intensities. The relative error was usually less than 10 per cent for most of the nucleotide units. In this way small differences in the band intensities may be demonstrated. They can be explained by variations of the local conformation of the biopolymer.