Single strand breaks SSBs encompass the disintegration of a single nucleotide and damaged 5 and or 3 termini. 9 Typical sources of SSBs include spontaneous hydrolysis leading to the formation of basic or apurinic apyrimidinic AP sites and further hydrolysis and oxidative damage by endogenous reactive oxygen species. ROS and ionizing radiation 10 SSBs can also be generated as intermediates of Endonuclease VIII like NEIL mediated BER and they can also arise as a result of chemical inhibition of cellular enzymes such as Top I 2 11 15. IR and free radicals generate two primary end groups at the 3 termini phosphate and phosphoglycolate whereas the primary end group at the 5 ends is phosphate 16. On the other hand damage by Top I inhibitors generate 3 phosphate and 5 OH termini. The removal of damaged bases by DNA glycosylases that possess an AP lyase activity generates 3 phosphate and 5 phosphate termini. 16 SSBs are considered a serious threat to genetic stability and cell survival If not repaired rapidly. Moreover, SSBs occur at a substantially higher frequency than double-strand breaks DSBs 17.
