After it is extracted from particular sources, nucleic acid must be stored either for archival purposes or before assay performance. The principle of nucleic acid storage is prevention of enzymatic or physical damage to the purified product. In order to overcome those problems we have three options of method to store our purified nucleic acid: chelating agents, chaotrophic agents, and refrigeration. When the solution contains RNA or high molecular-weight DNA, special care is needed.
In general, DNA can be stored effectively for long periods in a Tris-EDTA buffer at 4oC. The chelation of free divalent cations by EDTA or another chelating agent reduces the damage caused by contaminating nucleases, which require these cations for function. Further, cold temperatures reduce enzyme activity and improve nucleic acid stability. RNA, inherently more labile, should be stored at −80oC in a similar buffer. As an alternative, either DNA or RNA can be stored as an ethanol precipitate, with −20oC being the optimal storage temperature.
Should the nucleic acid sample remain contaminated with nuclease after purification attempts, the addition of chaotropic reagents like guanidium isothyocyanate (GITC) will deactivate remaining enzyme. GITC will crystallize at temperatures below room temperature, so solutions containing this reagent must be completely warmed before use. Likewise, RNA stored in a GITC-based solution should be kept at room temperature or frozen at −80oC. Those basic guidelines, purified DNA or RNA can be stored for long periods of time.