Method for the selective size-fractionated separation and isolation of nucleic acid mixtures

Abstract

The invention relates to a method for size-fractionated isolation of nucleic acids, characterized by the following steps: —a first binding buffer, which contains at least one chaotropic salt and at least one substance that raises the pH of the binding buffer, is added—in the absence of aliphatic alcohols—to a volume of the mixture of nucleic acids, —binding on a solid phase and separation of the nucleic acids bound by step a), —a second binding buffer, which has a lower pH than the binding buffer under Point a), or a nonionic surfactant or an alcohol or a mixture of nonionic surfactant and alcohol is mixed with the filtrate from step a), —binding on a solid phase and separation of the nucleic acids bound by step c), —washing and elution, according to known methods, of the nucleic acid isolated after steps a) and c), with the result that the nucleic acids isolated after step a) not only have a larger number of base pairs than the nucleic acids isolated under step c), but also that, both after both step a) and after step c), individual, particular nucleic acid fractions with a particular number of base pairs are isolated that were not isolated in the respective other step. The size ratios of the nucleic acid fractions can be controlled by changing the pH.