DIRECT MASS-SPECTROMETRIC SEQUENCING OF LOW-PICOMOLE AMOUNTS OF OLIGODEOXYNUCLEOTIDES WITH UP TO 21 BASES BY MATRIX-ASSISTED LASER-DESORPTION IONIZATION MASS-SPECTROMETRY

UV and IR matrix-assisted laser desorption/ionization mass spectrometr y (UV- and IR-MALDI) have demonstrated their potential for the accurat e and sensitive mass determination of oligonucleotides, Metastable mol ecule ion fragmentation was found to be the main limitation in both de sorption schemes for the analysis of Larger nucleic acid sequences. Fr agment ions from additional prompt decays, observed only in IR-MALDI, offer structural data, which allow sequence information to be derived for low-picomole amounts of oligodeoxynucleotides with up to 21 bases from a single mass spectrum, Two examples demonstrating the feasibilit y of this new sequencing technique are given, A model is introduced an d discussed, which proposes a reaction scheme for the observed fragmen t ion patterns of nucleic acids and differentiates prompt and metastab le fragmentation mechanisms. The role of fragmentation in direct mass spectrometric sequencing schemes and as a limitation for the accessibl e mass range in nucleic acid MALDI mass spectrometry is discussed.