Total steps. 3.
Step 1. and 2. are involved in the activation of the 5' phosphate in the nick.
AMP group is transferred to lysine amino acid in the first residue on the enzyme and later 5' phosphate in the nick of DNA strand.
Step 3. There is attack of 3' hydoxyl group on the phosphate, which causes the displacement of the AMP. and then the phosphodiester bond seals the strand.
