[Selective expression of a mutation of the rad 201 radiosensitivity gene in Drosophila embryogenesis].

Embryonic sensitivity to the lethal effect of gamma-irradiation was compared in a radiosensitive mutant strain rad201G1 and a control radioresistant strain of Drosophila during the first 9 h of embryonic development. Embryonic radiosensitivity was analyzed with regard to the physiological age of embryos at the time of exposure to radiation. In the wild-type embryos, age-dependent variations of radiosensitivity were shown to be closely associated with genetically determined alterations in mitotic cycle structure, synchronism, and duration of separate phases. The rad201 gene mutation, which disrupts repair of chromosome damage in female germ cells and somatic cells of Drosophila, is expressed selectively during the period studied. The mutation had no effect on lethality at the stages of cleavage division, which represent alternations of S and M phases of the cell cycle. However, it caused an increase in lethality at the stage of postblastodermal mitotic divisions, whose onset is associated with a transformation of the organization and functions of genetic material and the appearance of G2 in the cell cycle. This transformation seems to be required for the functioning of the repair system affected by rad201.