Molecular and structural characterization of the spindle pole bodies in the fission yeast Schizosaccharomyces japonicus var japonicus.

The structure and localization of the microtubule organization centres (MTOCs) of the fission yeast Schizosaccharomyces japonicus var. japonicus were examined by fluorescence microscopy and electron microscopy. Spindle pole bodies (SPBs), which are the fungal equivalent of centrosomes, of Sz. japonicus were visualized by immunofluorescent staining using a monoclonal anti-gamma-tubulin antibody. The behaviour of the SPBs during the cell cycle mostly coincided with previous reports on the most widely used fission yeast Schizosaccharomyces pombe. We cloned the gamma-tubulin gene from Sz. japonicus by PCR using redundant sets of primers corresponding to conserved regions of known gamma-tubulins. The predicted amino acid sequence of Sz. japonicus gamma-tubulin was most similar to the Sz. pombe gamma-tubulin. Under the electron microscope, the SPBs of Sz. japonicus were detected as electron-dense multilayered structures located just outside the nuclear envelope. The SPBs of Sz. japonicus were composed of three electron-dense layers and were surrounded by fuzzy material. Each layer showed structural changes according to the progression of the cell cycle. In mitotic cells, the SPBs were located on the fenestrae of the nuclear envelopes through which the mitotic spindle microtubules ran into the nucleoplasm. Our results show that Sz. japonicus is a very potent and attractive organism for the investigation of the microtubule nucleation system and morphogenesis in yeasts. The Accession No. for the nucleotide sequence of the Sz. japonicus gtb1(+) gene is AF159163.