When nucleic acid must be stored, either for archival purposes or before assay performance, the key goal is prevention of enzymatic or physical damage to the purified product. Three chief weapons are available for this endeavor: chelating agents, chaotrophic agents, and refrigeration. As discussed earlier, special care is needed when the solution contains RNA or high-molecular-weight DNA.
In general, DNA can be stored effectively for long periods in a Tris-EDTA buffer at 4°C. The chelation of free divalent cations by EDTA or another chelating agent diminishes the damage caused by contaminating nucleases, which require these cations for function. Cold temperatures further reduce enzyme activity and improve nucleic acid stability. RNA, inherently more labile, should be stored at -80°C in a similar buffer. As an alternative, either DNA or RNA can be stored as an ethanol precipitate, with -20°C being the optimal storage temperature.
Should the nucleic acid sample remain contaminated with nuclease after purification attempts, the addition of chaotropic reagents like 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 -80°C.
Following these basic guidelines, purified DNA or RNA can be stored for long periods of time.
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