Histone deacetylase inhibitor sodium butyrate enhances cellular radiosensitivity by inhibiting both DNA nonhomologous end joining and homologous recombination

► Sodium butyrate increases the radiosensitivity of HeLa cells. ► Sodium butyrate does not abrogate the gamma-radiation imposed G2 cell cycle arrest. ► Sodium butyrate obstructs both NHEJ and HR. ► A suggestion is made that an early step in DNA double strand breaks repair is a deacetylation of core histones and compaction of chromatin structure to keep the DNA ends close to each other.