[Appearance of single-stranded regions in DNA molecules in the G1 stage and the formation od structural mutations]

Single-stranded DNA regions in the nuclei of human lymphocytes were detected by means of fluorescent antibody technique. The frequency of fluorescent nuclei increased with the onset of the S stage, as expected. Also, a clear peak of the fluorescent nuclei amount was observed in about the middle of the G1 stage. The appearance of this peak correlated with some regularities of production of structural mutations by radiation. The suggestion is made that the maximum discovered might reflect the beginning of the recombinational repair of double-stranded breaks.