[en] Sedimentation in alkali was used to estimate the repair of X-ray-induced single strand breaks in the DNA of irradiated toluenized Escherichia coli cells in this study. Extensive repair requires no exogenous cofactors except ATP, although other individual NTPs (except U) or dNTPs can substitute for ATP. There is no repair in polA or resA cells and since nicotinamide mononucleotide (NMN) inhibits repair in wild type cells the results are interpreted as indicating that both ligase and polymerase I are needed for repair but that the amount of any gap filling is small and extensive repair replication is not necessary