By absorption measurements: at 260 nm with an UltrospecÒ
III UV/visible spectrophotometer (Pharmacia);
1 OD260 = 50 µg ds DNA
1 OD260 = 33 µg ss DNA
or
By comparing the fluorescence intensity of unknown DNA preparations with those of known amounts of l DNA after agarose gel electrophoresis and staining with ethidium bromide