Methods and compositions for the rapid isolation of small RNA molecules

1. A method for isolating small RNA from a biological sample, the method comprising:

a) contacting the biological sample with a chaotropic agent and a lithium salt, wherein large RNA and other macromolecules precipitate to form a debris but small RNA remains soluble, thereby forming a solution of soluble small RNA;

b) contacting the solution of soluble small RNA with a chromatographic binding matrix in the presence of at least one alcohol, such that the small RNA binds to the chromatographic binding matrix; and

c) eluting the small RNA from the chromatographic binding matrix, thereby isolating the small RNA.

2. The method of claim 1 , wherein contact with the chaotropic agent and the lithium salt occurs simultaneously or sequentially.

3. The method of claim 1 , wherein the chaotropic agent is chosen from guanidine hydrochloride, guanidine thiocyanate, guanidine carbonate, sodium perchlorate, sodium iodide, sodium trichloroacetate, and urea.

4. The method of claim 1 , wherein the lithium salt is chosen from lithium chloride, lithium acetate, lithium citrate, lithium carbonate, and lithium borate.

5. The method of claim 1 , wherein the chaotropic agent is guanidine hydrochloride and the lithium salt is lithium chloride.

6. The method of claim 1 , wherein the concentration of the chaotropic agent is from about 1 M to about 8 M and the concentration of the lithium salt is from about 1 M to about 8 M.

7. The method of claim 1 , wherein the chaotropic agent and the lithium salt are in a solution having a pH from about 3 to about 8.

8. The method of claim 1 , wherein the chaotropic agent and the lithium salt are in a solution having a pH from about 3 to about 4.

9. The method of claim 7 , wherein the solution further comprises at least one agent chosen from a detergent, a buffer, a thiol-reducing agent, an antifoaming agent, and a bulking agent.

10. The method of claim 1 , wherein the debris comprises precipitated large RNA molecules, genomic DNA molecules, protein molecules, and other macromolecules.

11. The method of claim 1 , further comprising a centrifugation step prior to step (b) wherein the solution of soluble small RNA is separated from the debris.

12. The method of claim 11 , further comprising a filtration step prior to step (b).

13. The method of claim 1 , wherein the alcohol is selected from the group consisting of methanol, ethanol, propanol, isopropanol, and butanol.

14. The method of claim 1 , wherein the concentration of alcohol is greater than about 50%.

15. The method of claim 1 , wherein the solution of soluble small RNA is contacted with 2 volumes of 100% ethanol during step (b).

16. The method of claim 1 , wherein the chromatographic binding matrix comprising the bound small RNA is washed with at least one wash solution prior to step (c).

17. The method of claim 16 , wherein the wash solution is chosen from a solution comprising from about 9 M to about 12 M of a salt and a solution comprising from about 80% to about 100% of alcohol.

18. The method of claim 1 , wherein the eluting of step (c) occurs in the presence of RNase-free water or RNase-free low salt buffer.

19. The method of claim 1 , wherein the small RNA is chosen from miRNA, siRNA, snRNA, snoRNA, smRNA, tasiRNA, rasiRNA, tncRNA, and scnRNA.

20. The method of claim 1 , wherein the small RNA is less than 200 nucleotides in length.

21. The method of claim 1 , wherein the small RNA is single stranded or double stranded.

22. The method of claim 5 , wherein the guanidine hydrochloride and the lithium chloride are provided in a solution have a pH from about 3 to about 4; the concentration of guanidine hydrochloride is from about 3 M to about 6 M; and the concentration of lithium chloride is from about 1.8 M to about 6 M.

23. The method of claim 22 , wherein the solution of soluble small RNA is contacted with 2 volumes of 100% ethanol during step (b).