【多选题】The basic pathway for repairing damage to DNA involves three basic steps:
A.
Step 1: excision: the damaged DNA is recognized and removed by one of a variety of mechanisms. These involve nucleases, which cleave the covalent bonds that join the damaged nucleotides to the rest of the DNA strand, leaving a small gap on one strand of the DNA double helix in the region.
B.
Step 2: resynthesis: a repair DNA polymerase binds to the 3ʹ-hydroxyl end of the cut DNA strand. It then fills in the gap by a complementary copy of the information stored in the undamaged strand.
C.
Step 3: ligation: when the repair DNA polymerase has filled in the gap, a break remains in the sugar–phosphate backbone of the repaired strand. This nick in the helix is sealed by DNA ligase, the same enzyme that joins the Okazaki fragments during replication of the lagging DNA strand.