The single-stranded viral DNA is isolated from M13mp18. M13mp18 is a M13 lac phage vector which contains single HindIII, SphI, SbfI, PstI, SalI (AccI/ HincII), XbaI, BamHI, SmaI (XmaI), KpnI (Acc65I), SacI and EcoRI sites within the gene encoding β-Galactosidase.This DNA preparation is useful as a standard and has been tested as a template in the dideoxy-nucleotide termination method of sequencing DNA.