Preparation of Single-Stranded Bacteriophage M13 DNA by Precipitation with Polyethylene Glycol

Bacteriophage M13 single-stranded DNA is prepared from virus particles secreted by infected bacteria into the surrounding medium. Several methods are available to purify the polymorphic filamentous particles. In this protocol, the particles are concentrated by precipitation with polyethylene glycol (PEG) in the presence of high salt. Subsequent extraction with phenol releases the single-stranded DNA, which is then collected by precipitation with ethanol. The resulting preparation is pure enough to be used as a template for DNA sequencing. A yield of 5–10 µg of single-stranded DNA/mL of infected cells may be expected from recombinant bacteriophages bearing inserts of 300–1000 nt.