DABA Fluorescence Assay for Submicrogram Amounts of DNA

The fluorescence assay of Kissane and Robins (1 ) is used to quantify deoxypurine nucleosides in crude mixtures. Acid-catalyzed depurination exposes the 1′ and 2′ carbons of deoxyribose, which can then form a strongly fluorescent compound with diaminobenzoic acid (DABA). DABA can react with all aldehydes of the form RCH₂ CHO, but deoxyribose is the predominant one in mammalian cells and essentially the only one in the acid or alcohol precipitates of aqueous extracts. Hence, no purification is required and RNA does not interfere. In our hands, the method is useful down to 30 ng of DNA, and probably could be made more sensitive, as discussed below. The method requires a visible-light fluorometer; the excitation wavelength is near 410 nm, with maximum fluorescence near 510 nm (2 ).