A NEW MASS-SPECTROMETRIC APPROACH TO DETECT MODIFICATIONS IN DNA

A new approach is described for the enzymatic digestion of DNA yieldin g oligonucleotides ranging from dinucleoside monophosphates to octanuc leoside heptaphosphates. DNA was digested by means of the benzon nudea se, an unspecific nuclease, and alkaline phosphatase to remove the ter minal phosphate. The mixture of oligonucleotides was separated using c apillary-zone electrophoresis with a buffer system, yielding a rather strong electro-osmotic flow. The oligomers are separated into groups w ith nucleotides of the same chain length. The separation capillary was used as the innermost capillary of an electrospray spraying system. N egative molecular ions of the nucleotides were recorded using a home-b uilt interface and ion source for a sector-field mass spectrometer. Th is approach allows the facile detection of DNA modifications since the y lead not only to differences in mass, but also can possess altered e lectrophoretic mobility. For modifying reactions which exhibit sequenc e specificity, the information is retained in the oligomers. Thus, rea ctions of DNA with electrophiles can be evaluated at different levels, since in longer chains, even complex sequence specificity may be appa rent. Results from calf thymus DNA digests and preliminary experiments with DNA adducts with styrene oxide are discussed.