Stabilized protease-containing solutions for purifying RNA-free DNA

A reagent mixture for purifying RNA-free DNA from a sample comprising DNA, RNA, and protein, the reagent mixture comprising:

• a protease, wherein the protease is present at a concentration of 0.5 mg/ml to about 7 mg/ml;
• an RNase;
• a detergent, and
• a buffering agent;
• wherein the reagent mixture is substantially free of cells or cell lysate and wherein the protease in the reagent mixture does not substantially inactivate the RNase when the mixture is stored for at least 24 hours at 4° C.