It has also been suggested that extracting a plant tissue lysate with chloroform first, before proceeding with RNA isolation, prevents the white, flocculent material from forming. PVP complexes with polysaccharide and polyphenol compounds commonly found in plants. The complexed material is centrifuged out of the lysate, and the lysate is then processed according to protocol. This step prevents carryover of contaminants that may inhibit downstream applications. Ambion's Plant RNA Isolation Aid is a solution of PVP that can be added to plant tissue lysates for removal of such contaminants.
Efficient homogenization is critical for reducing the effects of nucleases found in the tissues.
Pulverization of the spleen and thymus into small pieces on dry ice, under liquid nitrogen, allows for quick homogenization in lysis solution, which inactivates nucleases. The phenol extraction step of the tissue lysates can also present problems. The high DNA and RNA content of these tissues causes the homogenates to be unusually viscous. Extraction of such viscous homogenates sometimes results in incomplete phase separation. If a white precipitate forms immediately upon the addition of isopropanol, post-acid phenol extraction, this is a sign that DNA contamination is still present.