A method of isolating target nucleic acid molecules from a solution
comprising a mixture of different size nucleic acid molecules, in the
presence or absence of other biomolecules, by selectively facilitating
the adsorption of a particular species of nucleic acid molecule to the
functional group-coated surface of magnetically responsive paramagnetic
microparticles is disclosed. Separation is accomplished by manipulating
the ionic strength and polyalkylene glycol concentration of the solution
to selectively precipitate, and reversibly adsorb, the target species of
nucleic acid molecule, characterized by a particular molecular size, to
paramagnetic microparticles, the surfaces of which act as a bioaffinity
adsorbent for the nucleic acids. The target nucleic acid is isolated from
the starting mixture based on molecular size and through the removal of
magnetic beads to which the target nucleic acid molecules have been
adsorbed. The disclosed method provides a simple, robust and readily
automatable means of nucleic acid isolation and purification which
produces high quality nucleic acid molecules suitable for: capillary
electrophoresis, nucleotide sequencing, reverse transcription cloning the
transfection, transduction or microinjection of mammalian cells, gene
therapy protocols, the in vitro synthesis of RNA probes, cDNA library
construction and PCR amplification.