The modification can happen accidentally during replication fork collapse or in the response to ionizing radiation but also during controlled physiological processes such as V(D)J recombination.

Mutagenesis experiments have shown that the modification is necessary for the proper formation of ionizing radiation induced foci in response to double strand breaks, but is not required for the recruitment of proteins to the site of DSBs.

γH2AX can be detected as soon as 20 seconds after irradiation of cells (with DNA double-strand break formation), and half maximum accumulation of γH2AX occurs in one minute.

[11] The constitutive level of γH2AX expression in live cells, untreated by exogenous agents, likely represents DNA damage by endogenous oxidants generated during cellular respiration.

[12] The packaging of eukaryotic DNA into chromatin presents a barrier to all DNA-based processes that require recruitment of enzymes to their sites of action.

[15] On the one hand, overwhelming evidence supports a strong, quantitative correlation between γH2AX foci formation and DNA double-strand break induction following ionizing radiation exposure, based on absolute yields and distributions induced per unit dose.

[15] On the other hand, not only the formation of distinct γH2AX foci but also the induction of pan-nuclear γH2AX signals have been reported as a cellular reaction to various stressors other than ionizing radiation.

[16] γH2AX in undamaged chromatin is thought to possibly be generated via direct phosphorylation of H2AX by activated kinases, most likely diffusing from DNA damage sites.