Acridine orange staining of a single-stranded DNA bacteriophage

Sinsheimer's light-scattering experiments have established that the DNA of bacteriophage ΦX174 is in the single-stranded form. Our studies on purified concentrates of ΦX174 in the fluorescence microscope reveal staining characteristics with the fluorochrome acridine orange completely compatible with such a single-stranded DNA structure. Carnoy-fixed smears of viral concentrates developed a brilliant flame-red fluorescence. Treatment of similar smears with DNase prevented the development of this property while RNase had no effect. This staining property may prove a simple and direct means for detecting single-stranded DNA.