METHODS FOR THE EXTRACTION OF NUCLEIC ACID FROM A SAMPLE

The present invention relates to a method for extracting low molecular weight nucleic acid from a sample comprising a mixture of low molecular weight nucleic acid and high molecular weight nucleic acid, which comprises: (a) mixing the sample, a salt and a solid support capable of reversibly binding nucleic acid, thereby forming a first binding solution, wherein the salt is present at a concentration at which the high molecular weight nucleic acid selectively adsorbs to the solid support; (b) separating the solid support from the first binding solution, thereby yielding a fraction separated from the solid support; (c) mixing the fraction separated from the solid support in (b) with additional salt, whereby the salt is present at a higher concentration than that of the first binding solution in (a); (d) introducing additional solid support to the mixture in (c), thereby forming a second binding solution, wherein the low molecular weight nucleic selectively adsorbs to the additional solid support; and (e) separating the additional solid support from the second binding solution, thereby extracting low molecular weight nucleic acid from the sample, wherein the low molecular weight nucleic acid comprises less than 1200 base pairs and the high molecular weight nucleic acid comprises 1200 or more base pairs.