[Use of wolfram trioxide for setting off preparations of nucleic acids]

The use of tungsten trioxide for shadowing nucleic acids is shown to be possible. Approximately 20 mg of tungsten trioxide could be prepared by heating (25 s, 2 V) a coil (4 turns, 1.5 mm i.d.) made of tungsten wire 0.5 mm diameter in a vacuum evaporator at atmospheric pressure. As revealed by electron microscopy, this amount of tungsten trioxide is sufficient for qualitative rotary shadowing phage lambda DNA.