ANALYSIS OF THE SACCHAROMYCES SPINDLE POLE BY MATRIX-ASSISTED-LASER-DESORPTION IONIZATION (MALDI) MASS-SPECTROMETRY/

A highly enriched spindle pole preparation was prepared from budding y east and fractionated by SDS gel electrophoresis. Forty-five of the ge l bands that appeared enriched in this fraction were analyzed by high- mass accuracy matrix-assisted laser desorption/ionization (MALDI) pept ide mass mapping combined with sequence database searching. This ident ified twelve of the known spindle pole components and an additional el even gene products that had not previously been localized to the spind le pole. Immunoelectron microscopy localized eight of these components to different parts of the spindle. One of the gene products, Ndc80p, shows homology to human HEC protein (Chen, Y., D.J. Riley, P-L, Chen, and W-H. Lee. 1997. Mel. Cell Biol. 17:6049-6056) and temperature-sens itive mutants show defects in chromosome segregation. This is the firs t report of the identification of the components of a large cellular o rganelle by MALDI peptide mapping alone.