Methods and compositions for biotechnical separations using selective precipitation by compaction agents

Abstract

Preferred embodiments of the invention include purification of DNA, preferably plasmid DNA, by use of selective precipitation, preferably by addition of compaction agents. Also, included is a sealable method for the liquid phase separation of DNA from RNA. RNA may also be recovered by fractional precipitation according to the invention. Applicants have discovered that RNA, commonly the major contaminant in DNA preparations, can be left in solution while valuable purified plasmid DNA is directly precipitated. Additional aspects of the invention include mini-preps, preferably of plasmid and chromosomal DNA, to obtain sequenceable and restriction digestible DNA in high yields in multiple simultaneous procedures. Still further aspects disclose enhanced stripping of the compaction agent by a stripping method comprising high salt addition and pH shift, and combinations of these techniques. Also, disclosed is a method of assay in which a labeled probe is precipitated when it is hybridized to a target, (e.g. chromosomal DNA, oligonuclotides, Ribosomal RNA, tRNA), and thereafter precipitating the probe/target complex with compaction agents and leaving in solution any unhybridized probe. For example, chromosomal DNA, plasmid, ribosomal RNA, and oligonucleotides can be recovered in excellent purity; by then heating the mixture of nucleic acids (above their melting temperature if the hybridization site is buried within secondary structure) and thereafter precipitating the probe and the target.