Perform DNA extractions with this phenol:chloroform:isoamyl alcohol mixture (25:24:1), accompanied by a buffer to equilibrate the solution at either pH 6.7 or pH 8.0.
Sheared Salmon Sperm DNA is a very effective blocking agent when used in Northern prehybridization and hybridization buffers at a concentration of 100 to 200 μg/mL.