DIRECT-DETECTION OF SYNTHETIC AND BIOLOGICALLY GENERATED DOUBLE-STRANDED DNA BY MALDI-TOF MS

A synthetic 50-mer DNA was mixed at room temperature with a non-comple mentary or a complementary 27-mer and analyzed by matrix-assisted lase r desorption-ionization time-of-flight mass spectrometry. The former r esulted in negligible signals from a 27-/50- mer heterodimer; for the latter this was a dominant peak, consistent with maintaining Watson-Cr ick interactions in the gas phase. Double stranded DNA derived from an enzymatic digestion of a 252-base-pair polymerase chain reaction prod uct when prepared at room temperature yielded very little specific dou ble stranded DNA, but sample preparation at reduced temperature result ed in spectra dominated by the expected heterodimer signals with no ra ndom (i.e. non-Watson-Crick) dimers. As a DNA diagnostics genotyping a pplication, apolipoprotein-E alleles were easily distinguished conside ring only the masses of their double stranded DNA digest fragments. (C ) 1997 Elsevier Science B.V.