VIRAL CHARACTERIZATION BY DIRECT ANALYSIS OF CAPSID PROTEINS

Matrix-assisted laser desorption/ionization mass spectrometry has enab led viral coat proteins to be characterized directly from the virus. T his analysis, demonstrated here with tobacco mosaic virus U2, a bacter iophage MS2, and equine encephalitis TRD, is achieved with a combinati on of organic acid, W-absorbing matrix, and high-energy desorption wit h a nitrogen laser. The molecular weights of these proteins are determ ined with sufficient accuracy to allow differentiation among viral spe cies and strains. The abundant hydrophobic MS2 coat protein was analyz ed in aliquots of culture medium and of the tobacco mosaic virus coat protein in infected leaves. This method provides rapid detection of co at protein in the low-femtomole range, as estimated by titering plaque -forming units of MS2.