Defective mammalian cells isolated from x-irradiated cultures

Cultures of mammalian cells exposed to ionizing radiations give rise to a large proportion of surviving cells which express radiation injury in an heritable manner, in that isolated progency of irradiated cells that give rise to abnormally small colonies are found to grow more slowly and are more sensitive to further irradiation. Such inherited injury occurs in irradiated human as well as hamster cell lines. In two defective cell lines investigated, the enhanced radiation sensitivity was accompanied by reduced oxygen consumption. Defective Chinese hamster cell lines can exist with no visible gross alterations in karotype. The frequency of small colony appearance in irradiated normal cultures increases regularly with dose, and the frequency with which they are produced is apparently too great to be due to single-gene mutations.