Salmon sperm DNA

Denatured fragmented salmon sperm DNA should be used at a concentration of 100 μg/mL in prehybridization and hybridization solutions involving essentially any type of hybridization experiment. To prepare a solution of ~10 mg/mL:

• 1. Dissolve salmon sperm DNA (Sigma type III sodium salt) in H₂O at a concentration of 10 mg/mL. If necessary, stir the solution on a magnetic stirrer for 2-4 h at room temperature to help the DNA to dissolve.

• 2. Adjust the concentration of NaCl to 0.1 M, and extract the solution once with phenol and once with phenol:chloroform.

• 3. Recover the aqueous phase, and shear the DNA by passing it 12 times rapidly through a 17-gauge hypodermic needle.

• 4. Precipitate the DNA by adding 2 volumes of ice-cold ethanol, recover by centrifugation, and dissolve at a concentration of 10 mg/mL in H₂O.

• 5. Determine the A₂₆₀ of the solution and calculate the approximate concentration of the DNA.

• 6. Boil the solution for 10 min and store at −20°C in small aliquots. Just before use, heat the solution for 5 min in a boiling-water bath and chill quickly in ice water.