Matrix-assisted laser desorption/ionization mass spectrometry of DNA using photocleavable biotin

Oligonucleotides containing a photocleavable biotin (5'-PC-biotin) were analyzed by matrix assisted laser desorption/ionization mass spectrometry (MALDI-MS) with wavelengths in the ultraviolet (UV) and infrared (IR) from solution and after capture on streptavidin-coated agarose or magnetic beads. The analysis was used to monitor the release of the oligonucleotides as a result of photochemical cleavage of the biotinylated linker. Near-UV pulses (UV-MALDI) led to predominant release of the photocleaved product. In contrast, only the uncleaved analyte was detected using IR pulses (IR-MALDI). Results from MALDI analysis are also presented for DNA containing a photocleavable 5'-amino group which can be covalently linked to a variety of activated surfaces and marker molecules. In a demonstration of this approach, a 5'-PC-biotinylated 49 nt RNA oligonucleotide was enzymatically synthesized using a PC-biotin-r(AG) dinucleotide primer, captured on streptavidin coated magnetic beads and analyzed by UV-MALDI. Potential applications of photocleavable linkers combined with MALDI for the analysis of nucleic acids are discussed.