Protocol for blunting ends by 3' overhang removal and fill-in of 3' recessed (5' overhang) ends using DNA Polymerase I, Large (Klenow) Fragment (M0210) also provides an interactive version of this protocol where you can discover and share optimizations with the research community. 

  1. DNA should be dissolved in 1x NEBuffer or T4 DNA Ligase Reaction buffer supplemented with 33 μM each dNTP.
  2. Add 1 unit of Klenow per microgram DNA.
  3. Incubate for 15 minutes at 25°C.
  4. Stop reaction by adding EDTA to a final concentration of 10 mM and heating for 20 minutes at 75°C.