The mechanism of Spo11 DNA cleavage is as follows: A specific tyrosine side chain in the Spo11 protein attacks the phosphodiester backbone to cut the DNA and generate a covalent complex between the protein and the severed DNA strand .Two subunits of Spo11 cleave the DNA two nucleotides apart on the two DNA strands to make a staggered DSB.Spo11 shares this DNA cleavage mechanism with the DNA topoisomerases and the site-specificrecombinases.